Update watermark_remover.py

watermark_remover.py

@@ -87,6 +87,6 @@ def remove_watermark(image_bytes: bytes) -> tuple[bytes, str]:
         # Create output image
         out_img = Image.fromarray(data.astype(np.uint8), mode=img.mode)
         out_buffer = io.BytesIO()
-        out_img.save(out_buffer, format=img_format)
+        out_img.save(out_buffer, format="PNG")
         
-        return out_buffer.getvalue(), img_format
+        return out_buffer.getvalue(), "PNG"