These were so 'in' in the 90's. I stared cross-eyed into so many of these Magic Eye books when I was a kid, my nose pressed into the pages, it's no wonder I ended up needing glasses. These things made my eyes hurt--which, save for sticking something in them, is a rare occurrence. And even if I saw the hidden image, I could never figure out what it was.
Remember, blur your eyes, look "through" the picture...or something.