diff --git a/ROADMAP.md b/ROADMAP.md
index f9f2d2b..6acd347 100644
--- a/ROADMAP.md
+++ b/ROADMAP.md
@@ -22,6 +22,13 @@ they land.
   - [x] Status filter (matched / custom / unknown — not_found/deleted arrive with
         the e621 match cache)
 
+- [x] **Ephemeral similarity check** (`/similar`)
+  - [x] Drop a file: exact MD5 match, perceptual matches against the library,
+        and e621 IQDB candidates (auto-run for images)
+  - [x] Nothing enters the library: temp files are wiped on startup, after
+        `SIMILARITY_TTL_MINUTES` (default 30), on demand and by
+        `manage.py cleanup_similarity`
+
 ## 2. e621 integration
 
 - [x] **Download progress bar on the detail view**
@@ -116,6 +123,8 @@ Files now stage first and are resolved before entering the library.
 - [ ] Guest blacklist refresh on a timer (`refresh_guest_blacklist` via cron/systemd)
 - [ ] Follow sync on a timer (`sync_followed_tags` + `sync_followed_pools` via
       cron/systemd, e.g. every 30 minutes)
+- [ ] Similarity temp cleanup on a timer (`cleanup_similarity` via cron; the
+      TTL also cleans lazily when new checks are created)
 - [ ] Production setup: build the SPA, serve via Nginx (static + `/media` +
       `/library`), systemd unit for Waitress
 - [ ] Automated tests (backend API + frontend components)
diff --git a/backend/.env.example b/backend/.env.example
index b1e0fc7..1ee89e8 100644
--- a/backend/.env.example
+++ b/backend/.env.example
@@ -18,3 +18,7 @@ REDIS_URL=redis://127.0.0.1:6380/1
 # Redis by `manage.py refresh_guest_blacklist`.
 # GUEST_BLACKLIST_FALLBACK=young,cub,shota,loli,child,underage
 # GUEST_BLACKLIST_TTL=3600
+
+# Ephemeral similarity checks: temp files are wiped on startup and after
+# this many minutes.
+# SIMILARITY_TTL_MINUTES=30
diff --git a/backend/apps/library/apps.py b/backend/apps/library/apps.py
index 1a1d68e..a498075 100644
--- a/backend/apps/library/apps.py
+++ b/backend/apps/library/apps.py
@@ -1,5 +1,21 @@
+import logging
+
 from django.apps import AppConfig
 
+logger = logging.getLogger(__name__)
+
 
 class LibraryConfig(AppConfig):
     name = "apps.library"
+
+    def ready(self):
+        """Ephemeral similarity-check files never survive a restart."""
+        from . import similarity
+
+        try:
+            deleted = similarity.purge_similarity_files()
+        except OSError as exc:
+            logger.warning("Similarity file purge skipped: %s", exc)
+        else:
+            if deleted:
+                logger.info("Purged %s similarity file(s) on startup", deleted)
diff --git a/backend/apps/library/management/commands/cleanup_similarity.py b/backend/apps/library/management/commands/cleanup_similarity.py
new file mode 100644
index 0000000..81e3a05
--- /dev/null
+++ b/backend/apps/library/management/commands/cleanup_similarity.py
@@ -0,0 +1,46 @@
+from datetime import timedelta
+
+from django.conf import settings
+from django.core.management.base import BaseCommand
+from django.utils import timezone
+
+from apps.library.similarity import purge_similarity_checks
+
+
+class Command(BaseCommand):
+    help = (
+        "Delete ephemeral similarity-check files. By default removes checks "
+        "older than SIMILARITY_TTL_MINUTES; use --all to wipe every one."
+    )
+
+    def add_arguments(self, parser):
+        parser.add_argument(
+            "--minutes",
+            type=int,
+            default=None,
+            help="Delete checks older than N minutes "
+            "(default: the configured TTL, currently "
+            f"{getattr(settings, 'SIMILARITY_TTL_MINUTES', 30)}).",
+        )
+        parser.add_argument(
+            "--all",
+            action="store_true",
+            help="Delete every similarity check regardless of age.",
+        )
+
+    def handle(self, *args, **options):
+        if options["all"]:
+            deleted = purge_similarity_checks()
+            scope = "all"
+        else:
+            minutes = (
+                options["minutes"]
+                if options["minutes"] is not None
+                else getattr(settings, "SIMILARITY_TTL_MINUTES", 30)
+            )
+            cutoff = timezone.now() - timedelta(minutes=minutes)
+            deleted = purge_similarity_checks(cutoff)
+            scope = f"older than {minutes} minute(s)"
+        self.stdout.write(
+            self.style.SUCCESS(f"Deleted {deleted} similarity check(s) ({scope}).")
+        )
diff --git a/backend/apps/library/migrations/0010_similaritycheck.py b/backend/apps/library/migrations/0010_similaritycheck.py
new file mode 100644
index 0000000..8aff32f
--- /dev/null
+++ b/backend/apps/library/migrations/0010_similaritycheck.py
@@ -0,0 +1,33 @@
+# Generated by Django 6.1.1 on 2026-09-17 23:18
+
+import django.db.models.deletion
+import uuid
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('library', '0009_mediaitem_e621_checked_at_and_more'),
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='SimilarityCheck',
+            fields=[
+                ('id', models.UUIDField(default=uuid.uuid4, editable=False, primary_key=True, serialize=False)),
+                ('file', models.FileField(blank=True, upload_to='similarity/')),
+                ('original_filename', models.CharField(max_length=255)),
+                ('md5', models.CharField(blank=True, db_index=True, default='', max_length=32)),
+                ('size', models.BigIntegerField(default=0)),
+                ('results', models.JSONField(blank=True, default=dict)),
+                ('created_at', models.DateTimeField(auto_now_add=True)),
+                ('user', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='similarity_checks', to=settings.AUTH_USER_MODEL)),
+            ],
+            options={
+                'ordering': ['-created_at'],
+            },
+        ),
+    ]
diff --git a/backend/apps/library/models.py b/backend/apps/library/models.py
index 6176997..02f2c4a 100644
--- a/backend/apps/library/models.py
+++ b/backend/apps/library/models.py
@@ -281,3 +281,32 @@ class MatchTask(models.Model):
 
     def __str__(self):
         return f"Match scan {self.id} ({self.status})"
+
+
+class SimilarityCheck(models.Model):
+    """An ephemeral image uploaded only to check what it looks like.
+
+    Never enters the library: files live in the media temp folder and are
+    purged on startup, by the TTL and by `manage.py cleanup_similarity`.
+    """
+
+    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
+    user = models.ForeignKey(
+        settings.AUTH_USER_MODEL,
+        null=True,
+        blank=True,
+        on_delete=models.SET_NULL,
+        related_name="similarity_checks",
+    )
+    file = models.FileField(upload_to="similarity/", blank=True)
+    original_filename = models.CharField(max_length=255)
+    md5 = models.CharField(max_length=32, db_index=True, blank=True, default="")
+    size = models.BigIntegerField(default=0)
+    results = models.JSONField(default=dict, blank=True)
+    created_at = models.DateTimeField(auto_now_add=True)
+
+    class Meta:
+        ordering = ["-created_at"]
+
+    def __str__(self):
+        return f"Similarity check {self.id} ({self.original_filename})"
diff --git a/backend/apps/library/serializers.py b/backend/apps/library/serializers.py
index 60a2619..0dea0df 100644
--- a/backend/apps/library/serializers.py
+++ b/backend/apps/library/serializers.py
@@ -1,10 +1,19 @@
 import os
+from datetime import timedelta
 from pathlib import Path
 
+from django.conf import settings
 from django.core import signing
 from rest_framework import serializers
 
-from .models import MediaItem, MediaLocation, TempUpload, DownloadTask, MatchTask
+from .models import (
+    DownloadTask,
+    MatchTask,
+    MediaItem,
+    MediaLocation,
+    SimilarityCheck,
+    TempUpload,
+)
 from .services import (
     MEDIA_FILE_SALT,
     UPLOAD_FILE_SALT,
@@ -246,3 +255,45 @@ class MatchTaskSerializer(serializers.ModelSerializer):
             "updated_at",
         ]
         read_only_fields = fields
+
+
+class SimilarityCheckSerializer(serializers.ModelSerializer):
+    check_id = serializers.UUIDField(source="id", read_only=True)
+    file_url = serializers.SerializerMethodField()
+    expires_at = serializers.SerializerMethodField()
+
+    class Meta:
+        model = SimilarityCheck
+        fields = [
+            "check_id",
+            "original_filename",
+            "md5",
+            "size",
+            "file_url",
+            "results",
+            "expires_at",
+            "created_at",
+        ]
+        read_only_fields = fields
+
+    def _request_user(self):
+        request = self.context.get("request")
+        user = getattr(request, "user", None)
+        if user is None or not getattr(user, "is_authenticated", False):
+            return None
+        return user
+
+    def get_file_url(self, obj):
+        """Signed URL so <img> tags can preview the temporary upload."""
+        user = self._request_user()
+        if user is None or not obj.file:
+            return None
+        signature = signing.dumps(
+            {"check": str(obj.id), "user": user.id},
+            salt=UPLOAD_FILE_SALT,
+        )
+        return f"/api/similarity/{obj.id}/file/?sig={signature}"
+
+    def get_expires_at(self, obj):
+        ttl = int(getattr(settings, "SIMILARITY_TTL_MINUTES", 30))
+        return obj.created_at + timedelta(minutes=ttl)
diff --git a/backend/apps/library/similarity.py b/backend/apps/library/similarity.py
new file mode 100644
index 0000000..fc3ea72
--- /dev/null
+++ b/backend/apps/library/similarity.py
@@ -0,0 +1,159 @@
+"""Ephemeral similarity checks.
+
+A file lands in the media temp folder only long enough to answer "is this
+already in the library, and what does it look like on e621?". Nothing is
+indexed: files are deleted on startup, after the TTL, on request through the
+API, and by `manage.py cleanup_similarity` (for cron).
+"""
+
+import logging
+from datetime import timedelta
+from pathlib import Path
+
+from django.conf import settings
+from django.core import signing
+from django.utils import timezone
+from rest_framework import mixins, status, viewsets
+from rest_framework.decorators import action
+from rest_framework.parsers import FormParser, JSONParser, MultiPartParser
+from rest_framework.permissions import AllowAny, IsAuthenticated
+from rest_framework.response import Response
+
+from . import services
+from .models import MediaItem, SimilarityCheck
+from .serializers import SimilarityCheckSerializer
+from .tools import item_brief
+from .uploads import find_library_matches
+
+logger = logging.getLogger(__name__)
+
+TTL_MINUTES = int(getattr(settings, "SIMILARITY_TTL_MINUTES", 30))
+
+
+def purge_similarity_files():
+    """Delete every stored temp file without touching the database.
+
+    Safe to call during app startup (``AppConfig.ready``) — database rows are
+    removed lazily by ``purge_expired`` and the cleanup command.
+    """
+    root = Path(settings.MEDIA_ROOT) / "similarity"
+    if not root.exists():
+        return 0
+    deleted = 0
+    for path in sorted(root.rglob("*")):
+        if not path.is_file():
+            continue
+        try:
+            path.unlink()
+            deleted += 1
+        except OSError as exc:  # noqa: PERF203 - keep going past locked files
+            logger.warning("Could not delete %s: %s", path, exc)
+    for path in sorted(root.rglob("*"), reverse=True):
+        if path.is_dir():
+            try:
+                path.rmdir()
+            except OSError:
+                pass
+    return deleted
+
+
+def purge_similarity_checks(older_than=None):
+    """Delete checks (rows and files). ``older_than=None`` wipes them all."""
+    queryset = SimilarityCheck.objects.all()
+    if older_than is not None:
+        queryset = queryset.filter(created_at__lt=older_than)
+    deleted = 0
+    for check in queryset.iterator():
+        if check.file:
+            check.file.delete(save=False)
+        check.delete()
+        deleted += 1
+    return deleted
+
+
+def purge_expired():
+    """Remove checks past the TTL; called lazily before creating new ones."""
+    return purge_similarity_checks(timezone.now() - timedelta(minutes=TTL_MINUTES))
+
+
+class SimilarityCheckViewSet(
+    mixins.ListModelMixin,
+    mixins.RetrieveModelMixin,
+    mixins.DestroyModelMixin,
+    viewsets.GenericViewSet,
+):
+    """Check an upload against the library — exact MD5 plus visual matches."""
+
+    serializer_class = SimilarityCheckSerializer
+    permission_classes = [IsAuthenticated]
+    parser_classes = [MultiPartParser, FormParser, JSONParser]
+    http_method_names = ["get", "post", "delete", "head", "options"]
+
+    def get_queryset(self):
+        queryset = SimilarityCheck.objects.all()
+        user = self.request.user
+        if not (user.is_staff or user.is_superuser):
+            queryset = queryset.filter(user=user)
+        return queryset
+
+    def create(self, request):
+        upload = request.FILES.get("file")
+        if upload is None:
+            return Response(
+                {"detail": "A file is required."}, status=status.HTTP_400_BAD_REQUEST
+            )
+        extension = Path(upload.name).suffix.lower()
+        if extension not in services.ALLOWED_EXTENSIONS:
+            return Response(
+                {"detail": f"Unsupported file type: {extension or 'unknown'}"},
+                status=status.HTTP_400_BAD_REQUEST,
+            )
+
+        purge_expired()
+        check = SimilarityCheck.objects.create(
+            user=request.user,
+            file=upload,
+            original_filename=upload.name,
+            size=upload.size,
+        )
+        check.md5 = services.compute_md5(check.file.path)
+
+        exact = MediaItem.objects.filter(md5=check.md5).first()
+        matches = find_library_matches(check.file.path, limit=12, user=request.user)
+        if exact is not None:
+            exact_j_id = f"J-{exact.id}"
+            matches = [
+                match for match in matches if match.get("j_id") != exact_j_id
+            ]
+        check.results = {
+            "exact": item_brief(exact, request) if exact is not None else None,
+            "matches": matches,
+        }
+        check.save(update_fields=["md5", "results"])
+        return Response(
+            self.get_serializer(check).data, status=status.HTTP_201_CREATED
+        )
+
+    @action(detail=True, methods=["get", "head"], permission_classes=[AllowAny])
+    def file(self, request, pk=None):
+        """Serve the temp file; accepts a signed URL like staged uploads."""
+        check = None
+        if request.user.is_authenticated:
+            check = self.get_queryset().filter(pk=pk).first()
+        else:
+            signature = request.query_params.get("sig")
+            payload = None
+            if signature:
+                try:
+                    payload = signing.loads(
+                        signature, salt=services.UPLOAD_FILE_SALT, max_age=86400
+                    )
+                except signing.BadSignature:
+                    payload = None
+            if payload and payload.get("check") == str(pk):
+                check = SimilarityCheck.objects.filter(pk=pk).first()
+        if check is None or not check.file:
+            return Response(
+                {"detail": "Not found."}, status=status.HTTP_404_NOT_FOUND
+            )
+        return services.serve_file(request, check.file.path)
diff --git a/backend/apps/library/urls.py b/backend/apps/library/urls.py
index d1a35a8..39541b1 100644
--- a/backend/apps/library/urls.py
+++ b/backend/apps/library/urls.py
@@ -10,6 +10,7 @@ from .tools import (
     VisualGroupsView,
     VisualMatchesView,
 )
+from .similarity import SimilarityCheckViewSet
 from .uploads import TempUploadViewSet
 from .views import (
     ClientDownloadView,
@@ -23,6 +24,7 @@ router.register("files", MediaItemViewSet, basename="file")
 router.register("uploads", TempUploadViewSet, basename="upload")
 router.register("online/downloads", DownloadTaskViewSet, basename="download")
 router.register("matches", MatchTaskViewSet, basename="match")
+router.register("similarity", SimilarityCheckViewSet, basename="similarity")
 
 urlpatterns = [
     path("", include(router.urls)),
diff --git a/backend/config/settings.py b/backend/config/settings.py
index 9eb2cf0..3a1c68a 100644
--- a/backend/config/settings.py
+++ b/backend/config/settings.py
@@ -170,6 +170,10 @@ GUEST_BLACKLIST_TTL = int(os.getenv("GUEST_BLACKLIST_TTL", "3600"))
 # Similarity threshold for flagging staged uploads that match library items.
 VISUAL_MATCH_THRESHOLD = float(os.getenv("VISUAL_MATCH_THRESHOLD", "0.9"))
 
+# Ephemeral similarity-check uploads are deleted after this many minutes
+# (and always on startup).
+SIMILARITY_TTL_MINUTES = int(os.getenv("SIMILARITY_TTL_MINUTES", "30"))
+
 # Redis cache (run via docker compose at the repo root), shared by web
 # workers and management commands (e.g. the mirrored guest blacklist).
 CACHES = {
diff --git a/frontend/src/App.tsx b/frontend/src/App.tsx
index 6d7d5a7..04abc0c 100644
--- a/frontend/src/App.tsx
+++ b/frontend/src/App.tsx
@@ -22,6 +22,7 @@ import Md5Redirect from "@/features/library/Md5Redirect";
 import OnlinePage from "@/features/online/OnlinePage";
 import PoolDetailPage from "@/features/pools/PoolDetailPage";
 import PoolsPage from "@/features/pools/PoolsPage";
+import SimilarPage from "@/features/similar/SimilarPage";
 import UploadPage from "@/features/upload/UploadPage";
 import UsersPage from "@/features/users/UsersPage";
 import { isAgeVerified, markAgeVerified } from "@/lib/age";
@@ -107,6 +108,14 @@ export default function App() {
             </RequireAuth>
           }
         />
+        <Route
+          path="/similar"
+          element={
+            <RequireAuth>
+              <SimilarPage />
+            </RequireAuth>
+          }
+        />
         <Route
           path="/upload"
           element={
diff --git a/frontend/src/components/AppShell.tsx b/frontend/src/components/AppShell.tsx
index c636997..0c45a5d 100644
--- a/frontend/src/components/AppShell.tsx
+++ b/frontend/src/components/AppShell.tsx
@@ -62,6 +62,7 @@ export function AppShell() {
     { to: "/online", label: "Online" },
     { to: "/pools", label: "Pools" },
     ...(user ? [{ to: "/followed", label: "Followed" }] : []),
+    ...(user ? [{ to: "/similar", label: "Similar" }] : []),
     ...(user?.can_upload
       ? [
           { to: "/upload", label: "Upload" },
diff --git a/frontend/src/features/similar/SimilarPage.tsx b/frontend/src/features/similar/SimilarPage.tsx
new file mode 100644
index 0000000..e1eeb8e
--- /dev/null
+++ b/frontend/src/features/similar/SimilarPage.tsx
@@ -0,0 +1,492 @@
+import { useMutation, useQueryClient } from "@tanstack/react-query";
+import { ExternalLink, ImagePlus, Trash2, X } from "lucide-react";
+import {
+  useRef,
+  useState,
+  type ChangeEvent,
+  type DragEvent,
+} from "react";
+import { Link } from "react-router-dom";
+
+import { Button, Spinner } from "@/components/ui";
+import { api, errorMessage, uploadFile } from "@/lib/api";
+import { cn } from "@/lib/cn";
+import {
+  e621ErrorMessage,
+  effectiveCredentials,
+  iqdbSearch,
+  RATING_LABELS,
+  type E621IqdbResult,
+} from "@/lib/e621";
+import { formatBytes, formatDate } from "@/lib/format";
+import type { SimilarityCheck } from "@/lib/types";
+import { useE621 } from "@/store/e621";
+
+const VIDEO_RE = /\.(mp4|webm)$/i;
+
+const ratingPill: Record<string, string> = {
+  s: "bg-ctp-green text-ctp-crust",
+  q: "bg-ctp-peach text-ctp-crust",
+  e: "bg-ctp-red text-ctp-crust",
+};
+
+export default function SimilarPage() {
+  const queryClient = useQueryClient();
+  const credentials = useE621((state) => state.credentials);
+  const inputRef = useRef<HTMLInputElement>(null);
+
+  const [file, setFile] = useState<File | null>(null);
+  const [check, setCheck] = useState<SimilarityCheck | null>(null);
+  const [uploading, setUploading] = useState(false);
+  const [percent, setPercent] = useState(0);
+  const [error, setError] = useState<string | null>(null);
+  const [dragging, setDragging] = useState(false);
+
+  const [iqdb, setIqdb] = useState<E621IqdbResult[] | null>(null);
+  const [iqdbBusy, setIqdbBusy] = useState(false);
+  const [iqdbError, setIqdbError] = useState<string | null>(null);
+  const [selected, setSelected] = useState<E621IqdbResult | null>(null);
+
+  const configured = Boolean(credentials?.configured);
+
+  const deleteMutation = useMutation({
+    mutationFn: () =>
+      api(`/api/similarity/${check?.check_id}/`, { method: "DELETE" }),
+    onSuccess: () => {
+      setCheck(null);
+      setFile(null);
+      setIqdb(null);
+      setSelected(null);
+      setError(null);
+      setIqdbError(null);
+      if (inputRef.current) inputRef.current.value = "";
+    },
+  });
+
+  async function startCheck(selectedFile: File) {
+    setFile(selectedFile);
+    setCheck(null);
+    setIqdb(null);
+    setSelected(null);
+    setError(null);
+    setIqdbError(null);
+    setPercent(0);
+    setUploading(true);
+    try {
+      const data = await uploadFile<SimilarityCheck>(
+        selectedFile,
+        {},
+        setPercent,
+        "/api/similarity/",
+      );
+      setCheck(data);
+      void queryClient.invalidateQueries({ queryKey: ["files"] });
+    } catch (err) {
+      setError(errorMessage(err));
+    } finally {
+      setUploading(false);
+    }
+
+    if (VIDEO_RE.test(selectedFile.name)) return;
+    if (!configured) return;
+    setIqdbBusy(true);
+    try {
+      const results = await iqdbSearch(
+        effectiveCredentials(credentials),
+        selectedFile,
+        selectedFile.name,
+      );
+      setIqdb(results);
+    } catch (err) {
+      setIqdbError(e621ErrorMessage(err));
+    } finally {
+      setIqdbBusy(false);
+    }
+  }
+
+  function handleInput(event: ChangeEvent<HTMLInputElement>) {
+    const chosen = event.target.files?.[0];
+    if (chosen) void startCheck(chosen);
+  }
+
+  function handleDrop(event: DragEvent<HTMLDivElement>) {
+    event.preventDefault();
+    setDragging(false);
+    const dropped = event.dataTransfer.files?.[0];
+    if (dropped) void startCheck(dropped);
+  }
+
+  const isVideo = file ? VIDEO_RE.test(file.name) : false;
+  const exact = check?.results.exact ?? null;
+  const matches = check?.results.matches ?? [];
+
+  return (
+    <div className="mx-auto flex w-full max-w-6xl flex-col gap-6">
+      <header>
+        <h1 className="text-lg font-semibold">Similarity check</h1>
+        <p className="mt-1 text-sm text-ctp-overlay0">
+          Drop a file to see whether it is already in the library and what it
+          looks like on e621. Nothing is added to the library — the temporary
+          copy is deleted automatically after a while and on the next server
+          start.
+        </p>
+      </header>
+
+      <div
+        onDragOver={(event) => {
+          event.preventDefault();
+          setDragging(true);
+        }}
+        onDragLeave={() => setDragging(false)}
+        onDrop={handleDrop}
+        className={cn(
+          "flex flex-col items-center justify-center gap-2 rounded-lg border border-dashed px-6 py-10 text-center transition",
+          dragging
+            ? "border-ctp-mauve bg-ctp-mauve/10"
+            : "border-ctp-surface1 bg-ctp-base",
+        )}
+      >
+        <ImagePlus className="h-6 w-6 text-ctp-overlay0" />
+        <p className="text-sm text-ctp-subtext0">
+          Drag a file here, or{" "}
+          <button
+            type="button"
+            className="text-ctp-blue hover:underline"
+            onClick={() => inputRef.current?.click()}
+          >
+            choose one
+          </button>
+        </p>
+        <p className="text-[11px] text-ctp-overlay0">
+          Images get the full check (MD5, visual hashes, e621 IQDB); videos
+          only get the exact MD5 match.
+        </p>
+        <input
+          ref={inputRef}
+          type="file"
+          className="hidden"
+          onChange={handleInput}
+        />
+      </div>
+
+      {uploading ? (
+        <div className="flex items-center gap-3">
+          <div className="h-1.5 w-48 overflow-hidden rounded-full bg-ctp-surface0">
+            <div
+              className="h-full bg-ctp-mauve transition-all"
+              style={{ width: `${percent}%` }}
+            />
+          </div>
+          <span className="font-mono text-xs text-ctp-overlay0">
+            uploading… {percent}%
+          </span>
+        </div>
+      ) : null}
+
+      {error ? <p className="text-sm text-ctp-red">{error}</p> : null}
+
+      {check ? (
+        <div className="grid gap-6 lg:grid-cols-[320px_minmax(0,1fr)]">
+          <aside className="flex flex-col gap-4">
+            <section className="overflow-hidden rounded-lg border border-ctp-surface0 bg-ctp-base">
+              <div className="flex max-h-72 items-center justify-center overflow-hidden bg-ctp-mantle">
+                {check.file_url ? (
+                  isVideo ? (
+                    <video
+                      src={check.file_url}
+                      controls
+                      loop
+                      muted
+                      className="max-h-72 w-full object-contain"
+                    />
+                  ) : (
+                    <img
+                      src={check.file_url}
+                      alt={check.original_filename}
+                      className="max-h-72 w-full object-contain"
+                    />
+                  )
+                ) : null}
+              </div>
+              <div className="p-3">
+                <p
+                  className="truncate font-mono text-xs text-ctp-subtext1"
+                  title={check.original_filename}
+                >
+                  {check.original_filename}
+                </p>
+                <p className="mt-1 truncate font-mono text-[10px] text-ctp-overlay0">
+                  {check.md5}
+                </p>
+                <p className="mt-1 text-[11px] text-ctp-overlay0">
+                  {formatBytes(check.size)} · expires{" "}
+                  {formatDate(check.expires_at)}
+                </p>
+                <div className="mt-3 flex items-center gap-2">
+                  <Button
+                    variant="danger"
+                    className="px-2 py-1 text-xs"
+                    disabled={deleteMutation.isPending}
+                    onClick={() => deleteMutation.mutate()}
+                  >
+                    <Trash2 className="h-3.5 w-3.5" /> Delete now
+                  </Button>
+                  <Button
+                    variant="ghost"
+                    className="px-2 py-1 text-xs"
+                    onClick={() => {
+                      setCheck(null);
+                      setFile(null);
+                      setIqdb(null);
+                      setSelected(null);
+                      if (inputRef.current) inputRef.current.value = "";
+                    }}
+                  >
+                    <X className="h-3.5 w-3.5" /> Clear
+                  </Button>
+                </div>
+              </div>
+            </section>
+          </aside>
+
+          <div className="flex min-w-0 flex-col gap-6">
+            <section className="rounded-lg border border-ctp-surface0 bg-ctp-base p-4">
+              <h2 className="text-sm font-semibold text-ctp-subtext1">
+                In the library (exact MD5)
+              </h2>
+              {exact ? (
+                <Link
+                  to={`/detail/${exact.j_id}`}
+                  className="mt-3 flex items-center gap-3 rounded-md border border-ctp-green/40 bg-ctp-green/10 p-2 transition hover:bg-ctp-green/15"
+                >
+                  {exact.thumbnail_url ? (
+                    <img
+                      src={exact.thumbnail_url}
+                      alt={exact.j_id}
+                      className="h-14 w-14 rounded object-cover"
+                    />
+                  ) : null}
+                  <span className="min-w-0">
+                    <span className="block font-mono text-sm text-ctp-text">
+                      {exact.j_id}
+                    </span>
+                    <span className="block truncate text-xs text-ctp-overlay0">
+                      {exact.filename} · {formatBytes(exact.size)} ·{" "}
+                      {exact.location_count} cop
+                      {exact.location_count === 1 ? "y" : "ies"}
+                      {exact.e621_post_id
+                        ? ` · e621 #${exact.e621_post_id}`
+                        : ""}
+                    </span>
+                  </span>
+                </Link>
+              ) : (
+                <p className="mt-3 text-xs text-ctp-overlay0">
+                  Not in the library — no item has this MD5.
+                </p>
+              )}
+            </section>
+
+            <section className="rounded-lg border border-ctp-surface0 bg-ctp-base p-4">
+              <h2 className="text-sm font-semibold text-ctp-subtext1">
+                Visually similar in the library{" "}
+                <span className="font-mono text-[11px] text-ctp-overlay0">
+                  {matches.length}
+                </span>
+              </h2>
+              {isVideo ? (
+                <p className="mt-3 text-xs text-ctp-overlay0">
+                  Visual hashing works on images only.
+                </p>
+              ) : matches.length === 0 ? (
+                <p className="mt-3 text-xs text-ctp-overlay0">
+                  Nothing above the similarity threshold.
+                </p>
+              ) : (
+                <div className="mt-3 grid grid-cols-2 gap-3 sm:grid-cols-3 xl:grid-cols-4">
+                  {matches.map((match) => (
+                    <Link
+                      key={match.j_id}
+                      to={`/detail/${match.j_id}`}
+                      className="group overflow-hidden rounded-lg border border-ctp-surface0 bg-ctp-base transition hover:border-ctp-surface2"
+                    >
+                      <span className="relative block aspect-square overflow-hidden bg-ctp-mantle">
+                        {match.thumbnail_url ? (
+                          <img
+                            src={match.thumbnail_url}
+                            alt={match.j_id}
+                            loading="lazy"
+                            className="h-full w-full object-cover transition group-hover:scale-[1.03]"
+                          />
+                        ) : null}
+                        <span className="absolute right-2 top-2 rounded-sm bg-ctp-crust/80 px-1.5 py-0.5 font-mono text-[10px] text-ctp-subtext0">
+                          {match.similarity}%
+                        </span>
+                      </span>
+                      <span className="block px-2 py-1.5 font-mono text-[11px] text-ctp-subtext0">
+                        {match.j_id}
+                      </span>
+                    </Link>
+                  ))}
+                </div>
+              )}
+            </section>
+
+            <section className="rounded-lg border border-ctp-surface0 bg-ctp-base p-4">
+              <div className="flex items-center justify-between gap-2">
+                <h2 className="text-sm font-semibold text-ctp-subtext1">
+                  e621 IQDB
+                </h2>
+                {iqdbBusy ? (
+                  <span className="flex items-center gap-1.5 text-[11px] text-ctp-overlay0">
+                    <Spinner className="h-3 w-3" /> searching…
+                  </span>
+                ) : iqdb ? (
+                  <span className="font-mono text-[11px] text-ctp-overlay0">
+                    {iqdb.length} candidate(s)
+                  </span>
+                ) : null}
+              </div>
+
+              {isVideo ? (
+                <p className="mt-3 text-xs text-ctp-overlay0">
+                  IQDB works on images only.
+                </p>
+              ) : !configured ? (
+                <p className="mt-3 text-xs text-ctp-overlay0">
+                  <Link to="/account" className="text-ctp-blue hover:underline">
+                    Add e621 credentials
+                  </Link>{" "}
+                  to reverse-search this image on e621.
+                </p>
+              ) : iqdbError ? (
+                <p className="mt-3 text-xs text-ctp-red">{iqdbError}</p>
+              ) : iqdbBusy && !iqdb ? (
+                <div className="mt-3 flex justify-center py-4">
+                  <Spinner className="h-4 w-4" />
+                </div>
+              ) : iqdb && iqdb.length === 0 ? (
+                <p className="mt-3 text-xs text-ctp-overlay0">
+                  No similar posts found on e621.
+                </p>
+              ) : iqdb ? (
+                <>
+                  <div className="mt-3 grid grid-cols-3 gap-2 sm:grid-cols-4 xl:grid-cols-6">
+                    {iqdb.map((candidate) => {
+                      const isExact =
+                        candidate.md5 !== null &&
+                        check.md5 === candidate.md5;
+                      return (
+                        <button
+                          key={`${candidate.post_id}-${candidate.md5}`}
+                          type="button"
+                          disabled={candidate.post_id === null}
+                          onClick={() => setSelected(candidate)}
+                          className={cn(
+                            "overflow-hidden rounded-md border bg-ctp-mantle text-left transition",
+                            selected?.post_id === candidate.post_id
+                              ? "border-ctp-mauve ring-2 ring-ctp-mauve/40"
+                              : "border-ctp-surface0 hover:border-ctp-surface2",
+                          )}
+                        >
+                          <span className="relative block aspect-square overflow-hidden">
+                            {candidate.preview_url ? (
+                              <img
+                                src={candidate.preview_url}
+                                alt={`Post #${candidate.post_id}`}
+                                loading="lazy"
+                                className="h-full w-full object-cover"
+                              />
+                            ) : (
+                              <span className="flex h-full w-full items-center justify-center text-[10px] text-ctp-overlay0">
+                                No preview
+                              </span>
+                            )}
+                            {candidate.rating ? (
+                              <span
+                                className={cn(
+                                  "absolute left-1 top-1 rounded-full px-1 py-0.5 font-mono text-[9px] font-semibold uppercase",
+                                  ratingPill[candidate.rating] ??
+                                    "bg-ctp-surface1 text-ctp-text",
+                                )}
+                              >
+                                {candidate.rating}
+                              </span>
+                            ) : null}
+                            {isExact ? (
+                              <span className="absolute right-1 top-1 rounded-full bg-ctp-green/90 px-1 py-0.5 font-mono text-[9px] font-semibold uppercase text-ctp-crust">
+                                MD5
+                              </span>
+                            ) : null}
+                          </span>
+                          <span className="block px-1 py-0.5 font-mono text-[10px] text-ctp-overlay0">
+                            #{candidate.post_id}
+                            {candidate.score !== null
+                              ? ` · ${Math.round(candidate.score)}%`
+                              : ""}
+                          </span>
+                        </button>
+                      );
+                    })}
+                  </div>
+
+                  {selected ? (
+                    <div className="mt-3 rounded-md border border-ctp-surface0 bg-ctp-surface0/40 p-3">
+                      <p className="font-mono text-xs text-ctp-subtext1">
+                        Post #{selected.post_id}
+                      </p>
+                      <p className="mt-1 text-xs text-ctp-overlay0">
+                        {selected.rating
+                          ? (RATING_LABELS[selected.rating] ??
+                            selected.rating)
+                          : "Unknown rating"}
+                        {selected.score_total !== null
+                          ? ` · ▲ ${selected.score_total}`
+                          : ""}
+                        {selected.fav_count !== null
+                          ? ` · ${selected.fav_count} favs`
+                          : ""}
+                        {selected.width && selected.height
+                          ? ` · ${selected.width}×${selected.height}`
+                          : ""}
+                      </p>
+                      {selected.tags_preview.length > 0 ? (
+                        <div className="mt-2 flex flex-wrap gap-1">
+                          {selected.tags_preview.map((tag) => (
+                            <span
+                              key={tag}
+                              className="rounded border border-ctp-surface1 px-1 py-0.5 font-mono text-[10px] text-ctp-subtext0"
+                            >
+                              {tag}
+                            </span>
+                          ))}
+                        </div>
+                      ) : null}
+                      <div className="mt-3 flex items-center gap-3">
+                        <Link
+                          to={`/detail/${selected.post_id}`}
+                          className="inline-flex items-center gap-1.5 text-xs text-ctp-blue hover:underline"
+                        >
+                          <ExternalLink className="h-3.5 w-3.5" /> View post
+                        </Link>
+                      </div>
+                    </div>
+                  ) : (
+                    <p className="mt-2 text-[11px] text-ctp-overlay0">
+                      Select a candidate for its rating, score, favorites and
+                      tags.
+                    </p>
+                  )}
+                </>
+              ) : (
+                <p className="mt-3 text-xs text-ctp-overlay0">
+                  Waiting for the library check…
+                </p>
+              )}
+            </section>
+          </div>
+        </div>
+      ) : null}
+    </div>
+  );
+}
diff --git a/frontend/src/lib/api.ts b/frontend/src/lib/api.ts
index fc7b516..9b3f1a6 100644
--- a/frontend/src/lib/api.ts
+++ b/frontend/src/lib/api.ts
@@ -85,11 +85,12 @@ export async function api<T>(path: string, options: ApiOptions = {}): Promise<T>
   return (await response.json()) as T;
 }
 
-export function uploadFile(
+export function uploadFile<T = TempUpload>(
   file: File,
   fields: Record<string, string> = {},
   onProgress?: (percent: number) => void,
-): Promise<TempUpload> {
+  path = "/api/uploads/",
+): Promise<T> {
   return new Promise((resolve, reject) => {
     const form = new FormData();
     form.append("file", file);
@@ -98,7 +99,7 @@ export function uploadFile(
     }
 
     const request = new XMLHttpRequest();
-    request.open("POST", "/api/uploads/");
+    request.open("POST", path);
     const token = getToken();
     if (token) request.setRequestHeader("Authorization", `Token ${token}`);
     request.upload.addEventListener("progress", (event) => {
@@ -114,7 +115,7 @@ export function uploadFile(
         data = null;
       }
       if (request.status >= 200 && request.status < 300) {
-        resolve(data as TempUpload);
+        resolve(data as T);
       } else {
         reject(new ApiError(request.status, data));
       }
diff --git a/frontend/src/lib/types.ts b/frontend/src/lib/types.ts
index 31f562a..89ddef2 100644
--- a/frontend/src/lib/types.ts
+++ b/frontend/src/lib/types.ts
@@ -265,6 +265,20 @@ export interface FollowFeed {
   results: FollowFeedEntry[];
 }
 
+export interface SimilarityCheck {
+  check_id: string;
+  original_filename: string;
+  md5: string;
+  size: number;
+  file_url: string | null;
+  results: {
+    exact: DuplicateEntry | null;
+    matches: DuplicateEntry[];
+  };
+  expires_at: string;
+  created_at: string;
+}
+
 export interface FollowCloud {
   status: "ready" | "building";
   stale: boolean;