So to put it briefly google taught an AI to look for recognisable stuff within pictures. Fed it a whole lot of stuff in the form of animals, people, faces, cars, etc so that it might find them in patterns. Some tweaks of the code let it loop over and over, etc.
Essentially you can give it a starter image, or random fuzziness, and let it dream up whatever it can.
You can read more here. Worth a look.
ai.googleblog.com/2015/06/inceptionism-going-deeper-into-neural.html The results are pretty stunning. Not just because it's an AI actually "dreaming up" images, but also some of them are just stunning outright.
(some of them are also really trippy, or pretty dark, or as close to acid visuals as you'lll ever find..)
I thought I'd share some.