How to fix "The images are not in the right format" in App Store Connect

How to fix it

1. 1

   Read the real format from the first bytes

   Every image format starts with a fixed signature, so the first few bytes tell you what the file actually is regardless of its name.

   file screenshot.jpg
   # PNG image data, 1260 x 2736  <- renamed, not converted
   # JPEG image data, JFIF standard  <- genuinely a JPEG
   

   If file is not available, read the bytes directly. A PNG begins 89 50 4e 47, a JPEG begins ff d8 ff:

   xxd -l 4 screenshot.jpg
   

2. 2

   Re-encode instead of renaming

   Converting means decoding the pixels and writing them back out in the other format. A rename does neither.

   # macOS, no install needed
   sips -s format jpeg screenshot.png --out screenshot.jpg
   
   # ImageMagick, any platform
   magick screenshot.png -quality 95 screenshot.jpg
   

   Quality 90 to 95 is the usual range for store screenshots. Lower starts showing artefacts around text, which is the content that has to stay legible at gallery size.

3. 3

   Decide whether you need JPEG at all

   App Store Connect accepts .jpeg, .jpg and .png. PNG is not the problem on its own.

   Most people arrive here after hitting the alpha channel error and reaching for a rename as the fix. If that is the sequence you are in, converting to JPEG solves both at once, because JPEG has no alpha channel in the format. Keeping PNG also works as long as you strip the channel properly.

4. 4

   Check the set before uploading again

   Run the format check across the folder so a single renamed file does not cost you another round trip.

   for f in *; do
     printf "%s: " "$f"
     file -b "$f"
   done