Butt (Patreon)

Actually this is not the best example since it went rather well. It took me only 4 hours to do this which is a good score... Probably because there's no hands or feet visible. 

Look at the starting shapes, they were a disgusting piece of shit, I had no idea what to do but I had to start somewhere... I didn't erased it as the GIF could suggest but that was the jump in quality between two snapshots. It took few snapshots to define some okay shape and the further the process go, the less improvement is visible between snapshots and more details are being added until it hits a threshold where it stops improving and is rather just changing randomly – that's the threshold and a place where it stops.

It's looks like some kind of a genetic algorithm. The final quality of the picture is determined by how good the algorithm can judge if the current state of things is better or worse than before. When it hits the threshold it stops improving the picture because it simply can't decide which mutation in the current generation is the best one, so it ends up randomly changing lines but it can't improve it any further.

https://www.youtube.com/watch?v=ACjtE5zyihE 

This is a video showing 100000 generations of a genetic algorithm trying to draw Mona Lisa. It nails the basic outlines literally in the first second – you can already recognize the painting – then it is slowly refining it until it gets to a point where you can't see any improvement in next generations at all but rather some random changes – that's the point where the code determining how much a single specimen is similar to the actual painting fails – it's not precise enough to go any further.