This is what I get when I open desktop settings on the "Background" tab. The directory I have browsed to has pictures in it but they are not shown when selecting a desktop background.
Someone please help, I've had enough of the vanilla Xubuntu wallpaper.
file whattype.jpg
you'll see what type of images they are, and can check to see if they're compatible) You didn't give release details, so I can't provide more.