Taken from lightdm-webkit2-theme-arch to update it for JezerM's web-greeter.
This is a very minimal theme for lightdm's web-greeter which allows multiple users and chooses a random wallpaper each time. The wallpapers are from this reddit thread, you can even create your own one here!
You can put your own wallpapers in either /usr/share/web-greeter/themes/arch/wallpapers
or /usr/share/backgrounds/lightdm
You can also find this in the AUR.