The animated GIF has been a mainstay of the Internet since web pages could only have gray backgrounds and Creed was a popular band. The way they work is simple: two or more images are superimposed on each other and they switch back and forth on a timed loop. This gives the impression of sputtering animation. For some reason, in those early days, torches like this were very popular:
In any case, the practice of GIF making has changed a lot over the years. Now people like to capture celebrities doing weird things. These loops somehow make almost anything funny, even Cameron Diaz feeding Alex Rodriguez popcorn.
Stereographs presented two very similar images side-by-side. You looked at them through a special apparatus (the stereoscope) and it gave you a kind of 3D view of what you were looking at. They were so popular that Oliver Wendell Holmes (the more-famous Supreme Court justice's father) held in this very magazine that they -- not flat, 2D photographs -- were the true future of capturing images.
Because they appeared more solid, they were, therefore, more true.
A stereoscope is an instrument which makes surfaces look solid. All pictures in which perspective and light and shade are properly managed, have more or less of the effect of solidity; but by this instrument that effect is so heightened as to produce an appearance of reality which cheats the senses with its seeming truth.
The other thing you can do with these two side-by-side images is stack them atop one another and flip back and forth between them as in the classic animated GIF. And that is precisely what the new (still beta!) NYPL tool allows you to do.
I will warn you, though. There is something about the way stereographs animate that makes me a little sick to my stomach if I look at them for too long. For that reason, I'm not embedding any here, but you can take a look at a bunch of them at the NYPL site. And then you can try your hand at making one, perhaps of this "famous trotting ostrich," which has been hitched up for a jog around town.
And, of course, this is yet another very cool digital project form the NYPL, which we profiled last year for its innovative efforts online.
Images: 1. The Internet. 2. The Internet. 3. The New York Public Library.