Autostereograms are images designed to create a three-dimensional effect when viewed with both eyes. They consist of repeating patterns or textures that, when focused on correctly, reveal hidden depth and shapes. This effect occurs because the brain interprets the slight differences in the images seen by each eye. To view an autostereogram, a person must relax their eyes and look through the image rather than directly at it. This technique allows the brain to merge the two-dimensional patterns into a single 3D perception. Autostereograms gained popularity in the 1990s and are often used in visual puzzles and art.