On Linux the option Set command accepts a user defined one-liner to set the wallpaper if your system is not supported out of the box.
As a special case, one can tell Superpaper to use feh with a tested and built-in command by setting:
set_command=feh
In the custom command, replace '/path/to/img.jpg' by '{image}', i.e. for example with the Gnome command:
gsettings set org.gnome.desktop.background picture-uri file://{image}