It's requires both eyes I know that much (if I cover one the spinning stops), but I still don't understand exactly how it works - there will be some technical paper out there somewhere explaining it, hopefully I'll stumble across it eventually .

Talking of Magic Eyes pics I have an idea with them that should allow anyone to see the hidden image, even with little or no depth perception and none of that squinting, going cross eyed, sticking your nose on the screen type stuff. Got a fair bit of work to do before that idea becomes reality but I'll post the results if and when it works..