diff --git a/src/lib/components/ImageUpload.svelte b/src/lib/components/ImageUpload.svelte
index 35955d2..4cfecb6 100644
--- a/src/lib/components/ImageUpload.svelte
+++ b/src/lib/components/ImageUpload.svelte
@@ -1,7 +1,10 @@
 <script lang="ts">
 	import XIcon from 'lucide-svelte/icons/x';
+	import RefreshCw from 'lucide-svelte/icons/refresh-cw';
 	import type { Attachment } from '$lib/types/index.js';
 	import { optimizeImage } from '$lib/utils/image-optimize.js';
+	import { browser } from '$app/environment';
+	import { addPendingAttachment, type PendingAttachment } from '$lib/sync/idb.js';
 
 	interface Props {
 		noteId: string;
@@ -36,6 +39,34 @@
 			}
 			optimizing = false;
 
+			// Offline: store in IDB and display via blob URL
+			if (browser && !navigator.onLine) {
+				const tempId = crypto.randomUUID();
+				const pending: PendingAttachment = {
+					id: tempId,
+					noteId,
+					optimized,
+					thumbnail,
+					filename: file.name,
+					mimeType: optimized.type || file.type,
+					timestamp: Date.now()
+				};
+				await addPendingAttachment(pending);
+
+				const blobUrl = URL.createObjectURL(optimized);
+				onUpload({
+					id: tempId,
+					noteId,
+					filename: file.name,
+					mimeType: optimized.type || file.type,
+					size: optimized.size,
+					path: blobUrl,
+					pending: true,
+					createdAt: new Date()
+				} as Attachment & { pending: boolean });
+				continue;
+			}
+
 			uploading = true;
 			const formData = new FormData();
 			formData.append('file', new File([optimized], file.name, { type: optimized.type || file.type }));
@@ -74,13 +105,20 @@
 	{#if attachments.length > 0}
 		<div class="mb-2 flex flex-wrap gap-2">
 			{#each attachments as attachment}
+				{@const isPending = 'pending' in attachment && attachment.pending}
+				{@const imgSrc = isPending ? attachment.path : `/api/notes/${noteId}/attachments?attachmentId=${attachment.id}`}
 				<div class="group relative">
 					<img
-						src="/api/notes/{noteId}/attachments?attachmentId={attachment.id}"
+						src={imgSrc}
 						alt={attachment.filename}
-						class="h-20 w-20 rounded-sm object-cover"
+						class="h-20 w-20 rounded-sm object-cover {isPending ? 'opacity-70' : ''}"
 						data-testid="attachment-thumbnail"
 					/>
+					{#if isPending}
+						<div class="absolute bottom-0.5 left-0.5 rounded-sm bg-black/50 p-0.5" title="Pending sync">
+							<RefreshCw class="h-3 w-3 text-white" />
+						</div>
+					{/if}
 					<button
 						onclick={() => onRemove(attachment.id)}
 						class="absolute -right-1 -top-1 hidden rounded-full bg-[var(--destructive)] p-0.5 text-white group-hover:block"
diff --git a/src/lib/sync/client.ts b/src/lib/sync/client.ts
index e3dfe63..f4c5a92 100644
--- a/src/lib/sync/client.ts
+++ b/src/lib/sync/client.ts
@@ -1,6 +1,6 @@
 import { browser } from '$app/environment';
 import type { Note } from '$lib/types/index.js';
-import { putNote, getAllNotes, addToSyncQueue, getSyncQueue, clearSyncQueue, deleteNoteFromIdb, getMeta, setMeta } from './idb.js';
+import { putNote, getAllNotes, addToSyncQueue, getSyncQueue, clearSyncQueue, deleteNoteFromIdb, getMeta, setMeta, getPendingAttachments, removePendingAttachment } from './idb.js';
 import { mergeNotes } from './crdt.js';
 import { loadNotes, currentFilter } from '$lib/stores/notes.js';
 import { get } from 'svelte/store';
@@ -49,6 +49,31 @@ async function pushChanges(): Promise<boolean> {
 	}
 }
 
+/**
+ * Push pending offline attachments to server.
+ */
+async function pushPendingAttachments(): Promise<void> {
+	const pending = await getPendingAttachments();
+	for (const item of pending) {
+		try {
+			const formData = new FormData();
+			formData.append('file', new File([item.optimized], item.filename, { type: item.mimeType }));
+			formData.append('thumbnail', new File([item.thumbnail], `${item.filename}_thumb.webp`, { type: 'image/webp' }));
+
+			const res = await fetch(`/api/notes/${item.noteId}/attachments`, {
+				method: 'POST',
+				body: formData
+			});
+
+			if (res.ok) {
+				await removePendingAttachment(item.id);
+			}
+		} catch {
+			// Will retry on next sync cycle
+		}
+	}
+}
+
 /**
  * Pull remote changes and merge with local state.
  */
@@ -98,6 +123,7 @@ export async function sync(): Promise<void> {
 			return;
 		}
 
+		await pushPendingAttachments();
 		await pullChanges();
 		setStatus('synced');
 
diff --git a/src/lib/sync/idb.ts b/src/lib/sync/idb.ts
index c79d0f6..5d93a6f 100644
--- a/src/lib/sync/idb.ts
+++ b/src/lib/sync/idb.ts
@@ -2,7 +2,17 @@ import { openDB, type IDBPDatabase } from 'idb';
 import type { Note } from '$lib/types/index.js';
 
 const DB_NAME = 'crumbs';
-const DB_VERSION = 1;
+const DB_VERSION = 2;
+
+export interface PendingAttachment {
+	id: string;
+	noteId: string;
+	optimized: Blob;
+	thumbnail: Blob;
+	filename: string;
+	mimeType: string;
+	timestamp: number;
+}
 
 interface CrumbsDB {
 	notes: {
@@ -23,6 +33,13 @@ interface CrumbsDB {
 		key: string;
 		value: { key: string; value: string };
 	};
+	pendingAttachments: {
+		key: string;
+		value: PendingAttachment;
+		indexes: {
+			'by-noteId': string;
+		};
+	};
 }
 
 export interface SyncQueueItem {
@@ -58,6 +75,12 @@ export function getDb(): Promise<IDBPDatabase<CrumbsDB>> {
 				if (!db.objectStoreNames.contains('meta')) {
 					db.createObjectStore('meta', { keyPath: 'key' });
 				}
+
+				// Pending attachments (offline uploads)
+				if (!db.objectStoreNames.contains('pendingAttachments')) {
+					const pendingStore = db.createObjectStore('pendingAttachments', { keyPath: 'id' });
+					pendingStore.createIndex('by-noteId', 'noteId');
+				}
 			}
 		});
 	}
@@ -122,3 +145,22 @@ export async function setMeta(key: string, value: string): Promise<void> {
 	const db = await getDb();
 	await db.put('meta', { key, value });
 }
+
+// Pending attachment operations
+export async function addPendingAttachment(item: PendingAttachment): Promise<void> {
+	const db = await getDb();
+	await db.put('pendingAttachments', item);
+}
+
+export async function getPendingAttachments(noteId?: string): Promise<PendingAttachment[]> {
+	const db = await getDb();
+	if (noteId) {
+		return db.getAllFromIndex('pendingAttachments', 'by-noteId', noteId);
+	}
+	return db.getAll('pendingAttachments');
+}
+
+export async function removePendingAttachment(id: string): Promise<void> {
+	const db = await getDb();
+	await db.delete('pendingAttachments', id);
+}