There are many programs that can automatically refresh your desktop wallpaper but an increasing number are turning to Flickr to do so.
Fleace is one of the most discreet because it simply runs automatically at your system startup then terminates. Most other wallpaper changers minimize to the System Tray which can hog your RAM or use valuable resources but not Fleace.
Fleace chooses images at random based on Flickr tags that you specify, and usually it throws up some pretty interesting results. However, it can also display some real rubbish and occasionally, retrieval of the images can use up system resources, if only for a moment anyway. However, it does give you a preview Windows so you can choose whether to accept an image before it's used on your desktop.
Fleace is a really useful desktop wallpaper changer than takes advantage of the huge Flickr database without taking advantage of your system resources.