Remove a PNG alpha channel for App Store images

A PNG may look completely opaque while storing an alpha channel. Painting a white background does not necessarily change that file structure. The checker inspects the PNG color type and transparency metadata, rather than judging the thumbnail.

Fix the file, not just its appearance

1. Choose your PNG and the intended placement.
2. Open Preview & fix and choose a background. Transparent pixels will be composited over that color.
3. Choose PNG output and export the selected image. The encoder writes an RGB file without an alpha channel.

JPEG output is also opaque, but it uses lossy compression and is not accepted for the universal creative image preset. Keep an original copy of your artwork.

What gets checked again?

Each generated image is inspected before it enters the ZIP. Dimensions, actual file type and PNG alpha metadata must pass the selected preset. This does not check text, trademarks, age suitability or other content rules.

Source: Apple’s creative asset specifications. Apple’s restriction covers both alpha channels and transparency.