I loved these things when I was younger. I even tried to make one of my own by cutting an 8.5×11 piece of paper up and rearranging the puzzle pieces. I used to go on the Magic Eye website almost every day to see the new stereographic image they would have up. Riiiight up until my eyes started bleeding…
I was always pretty good at those things. Never had any problems with unfocusing my eyes to get the picture to pop out. It’s a pretty lame super power though.