From Fedora Project Wiki
The supplemental wallpaper submission period is open! We will be accepting wallpapers until August 9th 2011 at 23:59 UTC, so please, get your wallpaper submissions in! :)
Supplemental wallpapers are the non-default wallpapers provided with Fedora. Usually Fedora ships GNOME upstream supplemental wallpapers. We are going to collect a set of community-submitted wallpapers for Fedora 16. Still not sure what a supplemental wallpaper is? Look below at the wallpaper selection UI below - what appears in this dialog but is *Not* the default wallpaper is a 'supplemental' wallpaper.