Would you like to have your desktop background automatically change at regular intervals, say, every 20 minutes?  If you are using Windows 7 you can do that.  Here is how:

1. Put all of the images you want to use in the folder of your choice.
2. Close all windows and right click anywhere on the desktop.
3. Choose "Personalize".
4. Click "Desktop Background" in the lower left of your screen. You should see a big box, perhaps empty.
5. Drag all of the images you want to use into that box.
6. If they are not already selected, click the "Select All" button at upper right.
7. Click the box under "Picture position" and choose "Stretch".
8. Make your time interval choice with "Change picture every…”
9. Click Save changes at lower right.