MagicEye.js is not officially associated with the company that makes the books and posters that reveal hidden 3-D images, but it’s the same concept.
The code, which is currently a hit on GitHub, uses the HTML5 canvas element to generate what are called single image random dot stereograms–this is the visual nonsense that overlays the “hidden” image in Magic Eye posters. As a result, any image can be Magic Eyed, or at least you can trick people into defocusing their eyes and looking for secret three-dimensional messages on their screen.
The source code and detailed instructions on deploying it are available for developers, but if you’d rather skip right to the action there’s a browser-based demo of MagicEye.js. And if you get tired of the random, jagged shapes auto-generated by the code, there’s a button that lets you draw your own images in the browser too.