diff --git a/app/Http/Controllers/ServiceController.php b/app/Http/Controllers/ServiceController.php
index 24951c7..7c56c01 100644
--- a/app/Http/Controllers/ServiceController.php
+++ b/app/Http/Controllers/ServiceController.php
@@ -343,6 +343,20 @@ public function finalize(Service $service): JsonResponse
             'finalized_at' => now(),
         ]);
 
+        $resolver = app(\App\Services\ServiceImageResolver::class);
+        $keyVisual = $resolver->keyVisualFor($service);
+        $background = $resolver->backgroundFor($service);
+        $updates = [];
+        if ($keyVisual !== null && $service->key_visual_filename === null) {
+            $updates['key_visual_filename'] = $keyVisual;
+        }
+        if ($background !== null && $service->background_filename === null) {
+            $updates['background_filename'] = $background;
+        }
+        if ($updates !== []) {
+            $service->update($updates);
+        }
+
         return response()->json([
             'needs_confirmation' => false,
             'success' => 'Service wurde abgeschlossen.',
diff --git a/tests/Feature/FinalizeSnapshotTest.php b/tests/Feature/FinalizeSnapshotTest.php
new file mode 100644
index 0000000..37b66a3
--- /dev/null
+++ b/tests/Feature/FinalizeSnapshotTest.php
@@ -0,0 +1,91 @@
+<?php
+
+use App\Models\Service;
+use App\Models\Setting;
+use App\Models\User;
+use App\Services\ChurchToolsService;
+use App\Services\ServiceImageResolver;
+use Illuminate\Support\Carbon;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Storage;
+
+beforeEach(function () {
+    Storage::fake('public');
+});
+
+test('finalize nimmt snapshot des globalen hintergrunds wenn service spalte null ist', function () {
+    Storage::disk('public')->put('slides/bg1.jpg', 'fake-content');
+    Setting::set('current_background', 'slides/bg1.jpg');
+
+    $service = Service::factory()->create([
+        'background_filename' => null,
+        'finalized_at' => null,
+    ]);
+
+    $this->actingAs(User::factory()->create())
+        ->postJson(route('services.finalize', $service), ['confirmed' => true])
+        ->assertOk();
+
+    expect($service->fresh()->background_filename)->toBe('slides/bg1.jpg');
+});
+
+test('snapshot gewinnt: neuer globaler hintergrund beeinflusst abgeschlossenen service nicht', function () {
+    Storage::disk('public')->put('slides/bg1.jpg', 'fake-content');
+    Setting::set('current_background', 'slides/bg1.jpg');
+
+    $service = Service::factory()->create([
+        'background_filename' => null,
+        'finalized_at' => null,
+    ]);
+
+    $this->actingAs(User::factory()->create())
+        ->postJson(route('services.finalize', $service), ['confirmed' => true])
+        ->assertOk();
+
+    Storage::disk('public')->put('slides/bg2.jpg', 'fake-content');
+    Setting::set('current_background', 'slides/bg2.jpg');
+
+    $resolved = app(ServiceImageResolver::class)->backgroundFor($service->fresh());
+
+    expect($resolved)->toBe('slides/bg1.jpg');
+});
+
+test('cts sync ueberschreibt key_visual_filename und moderator_name nicht', function () {
+    Carbon::setTestNow('2026-03-01 09:00:00');
+
+    $service = Service::factory()->create([
+        'cts_event_id' => '424242',
+        'key_visual_filename' => 'custom.jpg',
+        'moderator_name' => 'Hans',
+        'preacher_name_override' => 'Pastor X',
+        'background_filename' => 'bg-custom.jpg',
+    ]);
+
+    $sync = new ChurchToolsService(
+        eventFetcher: fn () => [
+            new FakeEvent(
+                id: 424242,
+                title: 'Aktualisierter Titel',
+                startDate: '2026-03-08T10:00:00+00:00',
+                eventServices: [
+                    new FakeEventService('Predigt', new FakePerson('Neuer', 'Prediger')),
+                ],
+            ),
+        ],
+        songFetcher: fn () => [],
+        agendaFetcher: fn () => new FakeAgenda([]),
+        eventServiceFetcher: fn (int $eventId) => [
+            new FakeEventService('Predigt', new FakePerson('Neuer', 'Prediger')),
+        ],
+    );
+
+    $sync->sync();
+
+    $fresh = DB::table('services')->where('cts_event_id', '424242')->first();
+
+    expect($fresh->key_visual_filename)->toBe('custom.jpg');
+    expect($fresh->moderator_name)->toBe('Hans');
+    expect($fresh->preacher_name_override)->toBe('Pastor X');
+    expect($fresh->background_filename)->toBe('bg-custom.jpg');
+    expect($fresh->title)->toBe('Aktualisierter Titel');
+});