The creator calls it “animated optical illusions”, but that doesn’t seem right to me. It’s not actually an illusion, really.
Example here:
(for those who don't like unexplained links ... starting with what looks like a jumbled mess or "magic eye" picture, you draw a grid of black bars across it, it turns into an animated picture using a kind of strobe effect. Crappy example from my kitchen table here - it's actually quite easy to figure out how to make them. https://www.youtube.com/watch?v=AsGz-dJlpIk)
There’s a 2007 children’s book titled Gallop that uses this method to animate animals. In this book they call it “Scanimation”; a search for scanimation has lots of DIY links.