What do you call those pictures that you have to cross your eyes to see in 3D?

When you look at it from a normal distance, all you can see is the repetition of the same pattern... But then you either cross your eyes, and see the 3D picture appear in the middle. OR some people look at it from close, then slowly move the image further away from their eyes, and then they see the 3D image appear. Whats the name of those kinds of pictures?