A stereogram is a visual image designed to create the illusion of a three-dimensional scene from a two-dimensional picture. When viewed correctly, the brain perceives depth and shapes that are not immediately visible. This effect is achieved by using patterns or images that require the viewer to focus their eyes in a specific way. There are two main types of stereograms: autostereograms, which allow the 3D image to be seen without special glasses, and stereoscopic images, which require two slightly different images viewed simultaneously. Both types rely on the principles of binocular vision to create depth perception.