stereogram

A stereogram is a diagram or picture that creates an illusion of three-dimensionality. This effect is achieved by presenting two images of the same scene or object, taken from slightly different angles, to each eye separately. This technique, known as stereoscopy, relies on binocular vision, where the brain combines the two distinct images to perceive depth.123

Stereoscopic photographs, or stereographs, were very popular in the late 19th and early 20th centuries. They were viewed using a stereoscope, a device that allows each eye to see only its corresponding image, thus creating the 3-D effect. This technology has also been applied in areas like photogrammetry for measurements and in modern displays.425