Optical-illusion paint-by-numbers are fine-art painting kits for adults based on the optical-illusion and anamorphic artworks of Jonty Hurwitz. Unlike ordinary paint-by-numbers, the finished painting is itself an illusion, an image that plays with perception, depth or anamorphic distortion, so the act of painting it doubles as a lesson in how the illusion is built. The kits are designed for adult painters who want a genuine artwork at the end rather than a children's craft, and are available both directly from Sentient Art and as merchandise in science-museum gift shops that exhibit Hurwitz's work. They sit alongside the studio's anamorphic sculptures and nano-scale pieces as the accessible, hands-on entry point into the same ideas about perception and viewpoint.