With Wallpaper Master you can change your desktop wallpaper automatically and with a period you decide. You can create groups of wallpapers, using images from your own hard drive, and rotate images in these groups randomly. It can take up to 5000 photos per category!
You can also order or score wallpapers according to your tastes, and use keyboard shortcuts to more easily manage the program. In addition to indicating the change periods, obviously you can also change the wallpaper whenever you want just by clicking on the Wallpaper Master icon.