$ ls
Calibre Library Documents Images Pictures Scripts Wallpapers
Comics Downloads Isos Public Templates
Desktop Icons Music Screeny Videos
You can see where I put mine. I just point the Desktop Settings in right click on Desktop to my Wallpaper folder I made in /home/username and grab mine from there.
I leave /usr/share/backgrounds/xfce/ alone, unchanged.
Only in MacPup Puppy linux do I download and save extras in /usr/share/backgrounds since Puppy runs in root anyways, (which is not a problemo for me).