Google Wallpaper software takes a list of keywords or search phrases, it then downloads the related desktop backgrounds from Google Images and turns them in your XP wallpaper.
The wallpaper switcher lets you adjust the duration for which a wallpaper stays on your desktop and you can even block adult or porn images from entering your desktop by turning the Safe Search filter on. [but I doubt if that makes it 100% safe from downloading NSFW images]
PS: Like the Google Screensaver, Google wallpaper changer is created by some Google fan and they aren'nt from Googleplex.
Wallpaper AnAppADay [via Mark]