Autostereogram

It does works on LCDs. Funny enough, it didn't look like a shark at first to me; turns out my eyes overshot, and aligned two layers in, creating a quite different shape.

Here's the trick I recommend to train the eye muscles: practice the "magic floating finger" eye trick: https://michaelbach.de/ot/sze-Frankfurter/. As you alternate between looking at your finger trips, and looking at the distance, you can start to feel how focus controls the floating finger appearing and disappearing. This is the same thing with stereograms; you want to make two matching components overlap, at which point the eyes should snap it into place.

Position your index finger between your eyes and monitor. If you focus on your index finger you will see only one index finger, but if you focus on monitor you will see two index fingers. Now, you need to do the same thing with the monitor, i.e. you need to see two monitors :-) by looking somewhere behind the monitor. If you separate two monitors just enough you will see the shark in 3D.