A lenticular lens provides a 3D effect without glasses. At its simplest, it's the flip image that is occasionally on magazine or DVD covers (or if you're older, crackerjack premiums) where the angle you're looking at switches between the two images to provide limited motion. With current technologies, dozens of images can be placed under a lens to either present a short animation or a fairly convincing 3D effect where moving the image allows seeing around objects.

The trick is slicing up the image so that each image is a sliver that the lenticular lens sheet can deflect the correct line of the image to present the desired effect.  The lens isn't printed on. It's a plastic sheet that is placed over the printed image. There's nothing fancy about the printing. It's a question of having software to break up the different images that provide either motion or 3D.

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