Setting dynamic desktop images on GNOME
VincentNoel notes:
To change the background image with Gnome, you can use the commands
gconftool-2 -u \ /desktop/gnome/background/picture_filename gconftool-2 --type string --set \ /desktop/gnome/background/picture_filename $tmpdir/$IMAGEFILE
Use this command in the script from DynamicDesktopWithScript instead of display ... and it will work in Gnome.