What's it called when two photographs are printed on triangles so you see a different one from different angles?

Question

This is kinda hard to explain, but I've seen it several places before. I'm looking for a special way that two photographs are printed — they're printed so you from each angle can see just one of the two photos. It's printed on a load on triangles so if you're looking from 90 degrees you wouldn't really see anything, but from approximately 60 degrees and 120 degrees, you can see the two photos.

                 _________
                   /   \ 
   see photo two           see photo one

I'm looking for the name of this printing style. I hope it's explained so you can understand it.

Answer 1

This is known as lenticular printing.

From Wikipedia: How It Works

Each image is arranged (slicing) into strips, which are then interlaced with one or more similarly arranged images (splicing). These are printed on the back of a piece of plastic, with a series of thin lenses molded into the opposite side. Alternatively, the images can be printed on paper, which is then bonded to the plastic. With the new technology, lenses are printed in the same printing operation as the interlaced image, either on both sides of a flat sheet of transparent material, or on the same side of a sheet of paper, the image being covered with a transparent sheet of plastic or with a layer of transparent, which in turn is printed with several layers of varnish to create the lenses.

A close up of the surface of a lenticular printed 3D image.

To see how movement changes the image you see, this diagram shows it pretty effectively.