Ubuntu and spins' wallpaper packages

I have collected wallpapers that came from Mint's historical versions. Now I'm trying to collect those came from Ubuntu and its official spins' historical versions. (I really dislike these two non-free distributions. I'm glad to see that they are dying, slowly but surely...)

Briefly, browse the "universe" repository, and you'll find a lot of packages named "ubuntu-wallpapers-xxx.deb", where xxx is the codename of each version (e.g., "xenial" is the codename of 16.04 LTS, on which Trisquel 8 is based).

Download the deb packages (unlike Mint, I don't see any .tar.gz packages), and extract them using "ar x package.deb" command (first install the package "binutils", be sure to replace "package" with real package file names). You get a "data.tar.xz" package, and then use "tar Jxvf data.tar.xz" to extract it.