Update: see jollawall, a tool I made to create ambiance wallpapers for your Jolla.
I have been looking for a cool wallpaper for my Jolla. I found this site, but the wallpapers on there seems to be of a wrong resolution. I then found a blog post from JollaUsers explaining how to make ambiance wallpapers for the Jolla. The display has a resolution of 540 by 960 pixels, but since the wallpaper moves as you go from the lock screen to the home screen and the launcher, the resolution of the wallpaper should actually be 540 by 1600 pixels. I used JollaUsers template to make a few wallpapers. There is a sample below and a complete list of 9 wallpapers here.