Autostereograms are algorithmic images which allow people to see three-dimensional images by focusing on two-dimensional patterns. In the 90's stereograms, or "magic eye" images were popularized. When I mentioned them during a slide lecture in our Visual class I was surprised by the fact that very few students knew of them. Maybe I'm getting old.
If you're curious, click on the links below. Choose a fixed point in the center of the image and stare, allowing your eyes to relax or "blur". Eventually, you will see a three dimensional image appear. Be patient- it may take a while, and some people are simply unable to see them.