What is a stereogram?
The short definition, the main types, and a brief history from Wheatstone to the 1990s poster craze.
Stereogram guides
Short, plain guides to stereograms and hidden 3D pictures. New to them? Start with the step-by-step lessons, then come back here for the why and how.
How stereograms work
Why a repeating pattern turns into depth, and how an image is built from a depth map.
Parallel vs cross-eyed viewing
The two viewing methods, which one these puzzles use, and how to switch.
Why can't I see stereograms?
The usual reasons the picture will not appear, and what to try for each.
How to see stereograms on a phone
Holding distance, landscape mode and image size on small screens.