EDIT: nevermind, I had to change rockbox to display all files, not just supported ones. It works perfectly now, thanks for the help earlier robin.
Ok, I did that, but now I have another problem. The manual says to put it in the /.rockbox/backdrops directory if I want it to be saved as the backdrop. When I do that I can't find it on my ipod, so I put it both there and just inside the ipod drive (outside of the .rockbox folder). I can find it then on rockbox (it's just inside the "files" folder) and I can change the backdrop just fine, but when I turn the ipod off it won't come back on unless I do a soft reset, and the backdrop doesn't stay set. Any idea what the problem is now?