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..
I really hope it works. In 1984 I was the victim of a bottle attack which left me with a damaged nerve in the left side of my face. I now have a crooked smile and when my eyes relax, one turns upwards and as a result, I've never been able to see magic eye pics. I'd love to be able to.