Make product photo backgrounds pure white
Amazon and Walmart do not ask for a background that looks white. They ask for one that measures RGB(255,255,255). PrepShot produces that, and then checks it.
Why "looks white" gets rejected
A well-lit sweep photographs at 250 or 248, not 255. Light falls off across the frame, cameras protect highlights rather than clipping them, and JPEG compression can drag pixels near the subject off pure white after everything you did was correct. None of it is visible; all of it fails the check.
What PrepShot actually does
It separates the product from its backdrop, composites onto true white, and then decodes the finished file and reads the four corner pixels. Checking the encoded file matters: that is what the marketplace receives, and it is not always what the encoder was handed.
Two ways to get there
For photos on a plain backdrop: a lightbox or a seamless sweep, flood-filling inward from the frame edge is free, instant, and usually cleaner than anything cleverer. For photos on a busy background there is on-device segmentation, which needs a one-time 62MB download and never sends your photograph anywhere.
When it is unsure, it says so
Transparent glass, jewellery chains, mesh and wispy edges are where automatic cutouts go wrong. PrepShot scores each cutout against the photograph it came from and flags the doubtful ones for you to check, rather than shipping them quietly.