Eli5: How do magic eye pictures work.
Do this quick experiment. Look at something at least a few feet away from you, for example a wall on the far side of the room. Close one eye, and hold up your thumb so it covers something. Then close your open eye and open your closed eye. Now, your thumb is no longer covering the thing it was before.
The reason for this is [parallax](https://en.wikipedia.org/wiki/Parallax). Your eyes aren’t in exactly the same spot, so they each have a slightly different perspective. Your brain can combine the two different images to perceive a single scene with depth.
When you look at a regular picture, both eyes see the same thing, so you can’t perceive depth. But if you can take two pictures and make sure one eye sees one and the other eye sees the other you can recreate that sense of depth.
One way to do that is with a [stereoscope](https://en.wikipedia.org/wiki/Stereoscope) like a [view-master](https://en.wikipedia.org/wiki/View-Master). Another way is to put the two images side by side and then either cross your eyes (so your left eye is looking at the right image, and your right eye is looking at the left image), or look at a point that is far behind the image (this makes your left eye look at the left image and your right eye look at the right image).
That’s basically what a [magic eye image](https://en.wikipedia.org/wiki/Autostereogram) is, except instead of having two pictures side by side, the pictures overlap so you don’t have to move your eyes as much.
Wtf are you talking about?