Binary package “xwallpaper” in ubuntu focal

utility for setting image files as X wallpaper

 The xwallpaper utility allows you to set image files as your X wallpaper.
 JPEG, PNG, and XPM file formats are supported, all of them being configurable
 and therefore no fixed dependencies.
 .
 The wallpaper is also advertised to programs which support semi-transparent
 backgrounds.