My nephew is really into art and has been talking about stereoscopic vs. monocular vision to anyone who’ll listen lately.
Those magic eye pictures are, indeed, a stereoscopic vision thing. If you have two eyes but can’t see the picture, you may be one of the one in ten people who are stereoblind (it has something to do with the way your eyes work together).
My nephew is terribly disappointed that he is *not* stereoblind; apparently it’s an advantage in art. Being stereoblind is basically like closing one eye (for someone with normal stereoscopic vision) and apparently artists do that a lot do make sure that they are using monocular cues to give a sense of depth to their 2-D canvases.