Stereographs seem to be popping up everywhere at the moment, including at the New York Public Library which has created an online Stereogranimator.
A stereograph was one of the earliest innovations in 3D photography. It works by melding two near identical images through the use of a two-lensed apparatus called a stereoscope.
You can use the NYPL's Stereogranimator to create hypnotic, animated gifs or 3D anaglyphs (red and blue viewing specs required for the latter).
The stereographs (of which there are over 40,000, mostly dating from the 19th century) are fascinating in their own right, offering a romantic portal to another time.