diff --git a/apps/api/src/lib/media.ts b/apps/api/src/lib/media.ts
index 90ec41260..f1d99f112 100644
--- a/apps/api/src/lib/media.ts
+++ b/apps/api/src/lib/media.ts
@@ -57,6 +57,34 @@ export async function getMediaBuffer(
 	return { buffer, mimeType };
 }
 
+/**
+ * Download a media file normalized to plain RGB PNG, max `longestSide`
+ * pixels on its longer edge (default 1024). Uses mana-media's `/transform`
+ * endpoint, which pipes the original through `sharp` server-side — that
+ * handles HEIC from iPhones, palette-mode PNGs, CMYK JPEGs, weird color
+ * profiles, and other formats OpenAI's gpt-image-1 rejects with
+ * `invalid_image_file` or `Invalid image file or mode`.
+ *
+ * `fit=inside` preserves aspect ratio (no distortion on portrait/landscape
+ * refs) and only caps the longer side, which keeps payloads comfortably
+ * under OpenAI's 4 MB/image limit without losing reference fidelity.
+ */
+export async function getMediaBufferAsPng(
+	mediaId: string,
+	longestSide = 1024
+): Promise<{ buffer: ArrayBuffer; mimeType: 'image/png' }> {
+	const base = getMediaClient()
+		.getOriginalUrl(mediaId)
+		.replace(/\/file$/, '/transform');
+	const url = `${base}?format=png&w=${longestSide}&h=${longestSide}&fit=inside`;
+	const res = await fetch(url);
+	if (!res.ok) {
+		throw new Error(`mana-media transform failed for ${mediaId}: HTTP ${res.status}`);
+	}
+	const buffer = await res.arrayBuffer();
+	return { buffer, mimeType: 'image/png' };
+}
+
 /**
  * Verify that every id in `mediaIds` is owned by `userId` under one of
  * the given app scopes. Throws `{ status: 404, missing }` when any id
diff --git a/apps/api/src/modules/picture/routes.ts b/apps/api/src/modules/picture/routes.ts
index 156702963..e1757ac82 100644
--- a/apps/api/src/modules/picture/routes.ts
+++ b/apps/api/src/modules/picture/routes.ts
@@ -317,19 +317,21 @@ routes.post('/generate-with-reference', async (c) => {
 		return c.json({ error: 'Ownership check failed', detail: e.message }, 502);
 	}
 
-	// Fetch reference buffers in parallel. The mana-media /file route is
-	// public, so no auth header needed — ownership was already verified.
+	// Fetch reference buffers in parallel, normalized to clean RGB PNG via
+	// mana-media's transform endpoint. gpt-image-1 is picky about color
+	// modes and rejects HEIC / CMYK / palette-PNG / APNG with
+	// `Invalid image file or mode for image N` — routing through sharp
+	// server-side normalizes every upload before it hits OpenAI, and caps
+	// the longest side at 1024px to stay well under the 4 MB/image limit.
+	// No aspect-ratio distortion (fit=inside).
 	let referenceBlobs: Array<{ blob: Blob; filename: string }>;
 	try {
-		const { getMediaBuffer } = await import('../../lib/media');
-		const buffers = await Promise.all(refIds.map((id) => getMediaBuffer(id)));
-		referenceBlobs = buffers.map((b, i) => {
-			const ext = b.mimeType.split('/')[1]?.split(';')[0] ?? 'png';
-			return {
-				blob: new Blob([b.buffer], { type: b.mimeType }),
-				filename: `ref-${i}.${ext === 'jpeg' ? 'jpg' : ext}`,
-			};
-		});
+		const { getMediaBufferAsPng } = await import('../../lib/media');
+		const buffers = await Promise.all(refIds.map((id) => getMediaBufferAsPng(id, 1024)));
+		referenceBlobs = buffers.map((b, i) => ({
+			blob: new Blob([b.buffer], { type: b.mimeType }),
+			filename: `ref-${i}.png`,
+		}));
 	} catch (err) {
 		const message = err instanceof Error ? err.message : String(err);
 		console.error('[picture/generate-with-reference] failed to fetch reference media', {