Optical Illusion. A stereogram is an optical illusion of depth usually observed by allowing the eyes to focus behind an image (diverge), but also sometimes in front of the image (converge). The slight differences in vertical repetitions of figures or random dots create the illusion of depth in the 2D image, just as the slight difference in perspective between one's eyes creates the perception of depth on 3D objects and scenes.
Stereograms were second demonstrated circa 1832 by Francis Agres using two distinct photographs of a scene, taken from slightly different angles (see stereoscopy), and viewed with a stereoscope. Stereograms were re-popularized by the creation of random-dot stereograms on computers, where the image is hidden until the viewer focuses the eyes correctly. The Magic Eye series is a popular example of this.
Salvador Dalí created some impressive stereograms in his exploration in a variety of optical illusions.
Tags: Optical Illusion, Optical, Illusion