diff --git a/bun.lock b/bun.lock
index 9ab148e..d24d92a 100644
--- a/bun.lock
+++ b/bun.lock
@@ -42,6 +42,7 @@
         "remark-rehype": "^11.1.2",
         "resend": "^6.12.2",
         "serwist": "^9.5.11",
+        "sharp": "^0.34.5",
         "web-haptics": "^0.0.6",
       },
       "devDependencies": {
diff --git a/lib/image-processing.ts b/lib/image-processing.ts
new file mode 100644
index 0000000..f5ed3d3
--- /dev/null
+++ b/lib/image-processing.ts
@@ -0,0 +1,98 @@
+import sharp from "sharp"
+
+const MAX_WIDTH = 1920
+const MAX_HEIGHT = 1080
+const QUALITY_HIGH = 80
+const QUALITY_FLOOR = 75
+const MAX_SIZE_BYTES = 400 * 1024 // 400 KB
+const FALLBACK_WIDTH = 1280
+const FALLBACK_HEIGHT = 720
+
+const ALLOWED_MIME_TYPES = ["image/jpeg", "image/png", "image/webp"]
+
+// Magic byte signatures for file type validation
+const MAGIC_BYTES: Record<string, number[]> = {
+  "image/jpeg": [0xff, 0xd8, 0xff],
+  "image/png": [0x89, 0x50, 0x4e, 0x47],
+  "image/webp": [0x52, 0x49, 0x46, 0x46], // RIFF header (WEBP container)
+}
+
+export function validateMagicBytes(buffer: Buffer, declaredMime: string): boolean {
+  const expected = MAGIC_BYTES[declaredMime]
+  if (!expected) return false
+  if (buffer.length < expected.length) return false
+  return expected.every((byte, i) => buffer[i] === byte)
+}
+
+export function isAllowedMimeType(mimeType: string): boolean {
+  return ALLOWED_MIME_TYPES.includes(mimeType)
+}
+
+export interface ProcessedImage {
+  buffer: Buffer
+  width: number
+  height: number
+  mimeType: string // Always "image/jpeg" after processing
+  size: number
+}
+
+/**
+ * Process a screenshot for storage:
+ * 1. Validate format via magic bytes
+ * 2. Resize to max 1920×1080, maintain aspect ratio
+ * 3. Convert to progressive JPEG
+ * 4. If size > 400KB, reduce quality to 75
+ * 5. If still > 400KB at quality 75, resize to 1280×720 and try again
+ * 6. Strip ALL EXIF data
+ */
+export async function processScreenshot(
+  inputBuffer: Buffer,
+  declaredMime: string,
+): Promise<ProcessedImage> {
+  if (!isAllowedMimeType(declaredMime)) {
+    throw new Error(`Invalid MIME type: ${declaredMime}`)
+  }
+
+  if (!validateMagicBytes(inputBuffer, declaredMime)) {
+    throw new Error("File content does not match declared type")
+  }
+
+  let pipeline = sharp(inputBuffer, { animated: false })
+    .rotate() // Auto-rotate based on EXIF orientation
+    .resize(MAX_WIDTH, MAX_HEIGHT, { fit: "inside", withoutEnlargement: true })
+    .jpeg({ quality: QUALITY_HIGH, progressive: true, mozjpeg: true })
+    // Metadata is stripped by default (no .withMetadata() / .keepMetadata() call)
+
+  let outputBuffer = await pipeline.toBuffer()
+  let metadata = await sharp(outputBuffer).metadata()
+
+  // If still over 400KB, reduce quality to floor
+  if (outputBuffer.length > MAX_SIZE_BYTES) {
+    pipeline = sharp(inputBuffer, { animated: false })
+      .rotate()
+      .resize(MAX_WIDTH, MAX_HEIGHT, { fit: "inside", withoutEnlargement: true })
+      .jpeg({ quality: QUALITY_FLOOR, progressive: true, mozjpeg: true })
+
+    outputBuffer = await pipeline.toBuffer()
+    metadata = await sharp(outputBuffer).metadata()
+  }
+
+  // If STILL over 400KB, downscale to 1280×720
+  if (outputBuffer.length > MAX_SIZE_BYTES) {
+    pipeline = sharp(inputBuffer, { animated: false })
+      .rotate()
+      .resize(FALLBACK_WIDTH, FALLBACK_HEIGHT, { fit: "inside", withoutEnlargement: true })
+      .jpeg({ quality: QUALITY_FLOOR, progressive: true, mozjpeg: true })
+
+    outputBuffer = await pipeline.toBuffer()
+    metadata = await sharp(outputBuffer).metadata()
+  }
+
+  return {
+    buffer: outputBuffer,
+    width: metadata.width ?? FALLBACK_WIDTH,
+    height: metadata.height ?? FALLBACK_HEIGHT,
+    mimeType: "image/jpeg",
+    size: outputBuffer.length,
+  }
+}
\ No newline at end of file
diff --git a/package.json b/package.json
index 55bed21..a943c11 100644
--- a/package.json
+++ b/package.json
@@ -53,6 +53,7 @@
     "remark-rehype": "^11.1.2",
     "resend": "^6.12.2",
     "serwist": "^9.5.11",
+    "sharp": "^0.34.5",
     "web-haptics": "^0.0.6"
   },
   "devDependencies": {