Yes, white backgrounds are mandatory for any photos that serve a "primary" purpose. For example, primary part photos, form photos, and product front/back photos all require a white background. A black background can be used for photos, but only for those photos that serve only as gallery ("non-primary") photos. Basically, for all important photos, a white background is required. Having said that, photos with black backgrounds can be accepted but will not serve as primary photos.
Regarding size, your photos are coming through much smaller than 1MB...for example, the photos you submitted for Police Robo are 176K and 184K. The Shuttle Robo front and back photos are 153K and 174K, respectively.
MIKE
engledogg