hologram

Did You Know? If you tear an ordinary photograph in two, each piece shows only a part of the original image. If you break a hologram in two, however, you end up with two holograms, each of which shows the entire original scene, although from slightly different points of view. That's because each spot on a hologram contains enough information to show how the entire scene would look if it were viewed from a particular vantage point. Imagine looking at a room through a peephole set in a solid door. What you see depends on where in the door the peephole is placed. Each piece of the hologram is a "peephole" view, and that's what makes the image look three-dimensional: as you move the hologram around or look at different parts of it, you see the original object from different angles, just as if it were a truly three-dimensional object and you were walking around it. The amount of information contained in holograms makes them very useful. They are much harder to copy than simple two-dimensional images, since to forge a hologram you'd have to know what the original object looked like from many angles. That's why credit cards, CDs, sports memorabilia, and other items include holographic stickers as indicators of authenticity.