A recent submission to Wincustomize met with queries/concerns regarding the use of an image as background wallpaper in displaying the Application Skin.
If you upload a skin, icon, cursor, whatever to the site and display it/them on a background which is NOT of your making it would be most appropriate to post credit for the wallpaper/image used, and, more importantly indicate the wall/image is NOT included within the skin submission/archive.
If on the other hand the image/wall IS INCLUDED please do not forget to again post credit AND include permission for its use within the submission archive. 