Ok, I take back what I said about the magic eye images. I thought you had to cross your eyes to align the fields, but then I went and googled how they actually work. Crossing your eyes can work but so can just holding the picture at the right distance and focusing your vision “through” the picture (like you’re looking at something further away behind it.

But either way,it takes some kind of skill and muscle control of your vision (which isn’t necessarily related to the quality of your vision…) to make it work. As opposed to movies where you wear the glasses and they do the work for you.