That's what it's supposed to be. The explanation assumes you already know what an "autostereogram" is and know how to look at them. There is a trick involved where you focus your eyes on a point somewhere in space behind the screen instead of on the screen, and it suddenly acquires depth.

https://en.wikipedia.org/wiki/Autostereogram will tell you more about this.

That's correct -- if you cross your eyes correctly, you should see some 3D depth in the static.

http://www.magiceye.com/faq_example.htm has some helpful instructions (you're looking for a planet with rings)

Would be useful if it had some markers for achieving the correct amount of focus.

I've never been able to see these things.

In this example, I always see two squares when trying to look behind it, never 4 like the instructions require.

How can I let my eyes focus behind the screen? I can focus my eyes in front of it by looking at my finger, and get 4 squares that way, but that doesn't work for focusing behind it, for me.

No planet appears when making it 3 squares while looking at finger in front of it either for me. And if I remove my finger, my eyes immediately change their focus :/

Any tips?

No tips - except at a guess 10 or 20% can't and won't ever see them.

I spent ages trying to make these things work in the 80s or 90s whenever the posters were the craze. Never got close, and there were quite a few others they simply didn't work on.

Now you're just bringing back memories of the mid 90s and people giving 'helpful' suggestions of how to see the images. I still can't see them.

Could be used for stereogram steganography!

Yes. That's expected. It's a Magic Eye style stereogram. If you make your eyes do the Magic Eye "thing", you can see the 3D shapes in the world and use the arrow keys to move around.

Press 1 or 2, and it will render in normal 3D

I see a sailboat!