Weird Images
To begin with, not all the images here are true stereograms, the exception being the one with the swirls that causes motion to be perceived where none is possible. That still leaves the question: what is a stereogram? The simplest answer is, that it is any image or set of images on a two-dimensional surface that, when viewed, result in a three-dimensional effect. At the beginning of the 20th Century, such images were all the rage. Two images were mounted on a card, and that was placed in a 'viewer' that had a pair of lenses, and was held up to the eyes. In the 50s the View-Master (still available - click here) was a great toy for kids to wonder over.
Hope there's some 'kid' left in you, and that you find these fun!