Magnus - Shazam for art
Muzei - Muzei is a live wallpaper that gently refreshes your home screen each day with famous works of art.
Artsy - A global platform for discovering and collecting art.
Variety Wallpaper Changer - Variety is a wallpaper changer for Ubuntu which is featureful, yet slim and very easy to use.
SINGULART - World's Leading Online Art Gallery
John's Background Switcher - Switch backgrounds to trending imgur, reddit, tumblr threads