diff --git a/webview-ui/src/utils/image.ts b/webview-ui/src/utils/image.ts
new file mode 100644
index 0000000000..2fa737df33
--- /dev/null
+++ b/webview-ui/src/utils/image.ts
@@ -0,0 +1,16 @@
+/**
+ * Utilities for image handling in webview.
+ */
+export const MAX_IMAGE_BYTES = 10 * 1024 * 1024
+
+/**
+ * Estimate raw bytes from a base64 data URL. Returns 0 for invalid input.
+ */
+export function estimateBytesFromBase64DataUrl(dataUrl: string): number {
+	if (typeof dataUrl !== "string") return 0
+	const idx = dataUrl.indexOf(",")
+	if (idx === -1) return 0
+	const base64 = dataUrl.slice(idx + 1).replace(/=+$/, "")
+	// 4 base64 chars represent 3 bytes
+	return Math.floor((base64.length * 3) / 4)
+}