There can be, and are issues with copyrighted images. For example, StarWars is Lucas Arts, and Star Trek is Gene Roddenberry [or his estate, to be more accurate].
Celebrity Photoskins have the issue of the true public availability of the photo image that is used....unless taken by the artist himself, it is the property of the photographer and permission should be obtained for its use.
So...
Certain wallpaper submissions, although slipping through the moderation net on occasion, will not be deemed appropriate, and will be removed.
Uploading one or two Wallpapers to WinCustomize to spotlight your artistic talents is good. Uploading even a dozen or so of diverse subject matter and style is also good.
When the submission number reaches 79, the chances are that not all are likely to remain.
Wallpapers are seen as an adjunct to the themes and skins hosted, to compliment them, not to swamp the site, rendering WinCustomize a repository for walls to the ultimate detriment of the other sections....