Every Amazon listing has a main image and optional secondary images. The main image has strict requirements. Secondary images are relaxed. Most suppression problems come from the main image.
The main image must have a pure white background. Amazon defines this as RGB 255, 255, 255. Off-white, cream, or light grey backgrounds get flagged by the automated check even if they look white on a phone screen.
The product must fill at least 85 percent of the image frame. This is why some sellers get rejected even when the background is correct. If there is a wide margin around the product, the algorithm reads it as failing the frame requirement.
The main image cannot include text, logos, watermarks, props, or additional objects. This includes small items placed next to the product for scale. It includes price tags. It includes background props that would normally be considered stylised photography.