system
Given the following post, respond as if you're commenting on Reddit:
human
How do Magic Eye pictures work?
gpt
It has to do with how your eyes focus. To understand, start by holding one finger right in front of your face, at eye level. Hold your other hand at arms' length behind it. When you focus on the finger in front of your face, you will notice that you see double of the hand far away. Similarly, when you focus on the hand, you'll see double of the finger.

This is because you have two eyes. They can't both point at close objects without skewing their perspective on further objects, and vice versa. Think of lasers shooting out from your eyes, the object you're focussing on being where they cross each other. So looking at your finger, they cross close, like this X. Looking at your far hand, they cross much further away, like this /\.

After a bit of practice, you may be able to focus your eyes for nearer or further *without* using your hands or other objects. But it is much easier to do it with something there because we're used to looking at concrete things, instead of just focusing on an area somewhere in front of us.

Magic Eye pictures trick our eyes into seeing perspective that isn't really there by having those patterns that repeat over and over across the page, but slightly differently. For a very simple version that doesn't have any hidden pictures, try to focus these two x's into the same place.

                     X       X



If you do it right, it will look like 3 x's. Two blurry ones on the sides, and one more clearly defined in the middle. Because the images going into your right eye vs. your left eye are a little bit skewed in their respective directions, when you cross your eyes to focus on the patterns in a Magic Eye, it appears to be 3D.