Each image is assigned a 'rule', which is a set of numbers between 0 and 8. Hover an image to see its rule. Each image starts white, with a single black pixel in the center, then, random pixels are picked, one by one. For each pixel, we check the number of its neighbouring pixels which are already black. If that number is in the image rule, we color that random pixel black.
The image below represent all rules, except those which does not include 0 and 1, as those rules could never fill a single pixel. Some rules produce the same exact result. (Notice that the random pick of pixels is the same for all images). The first two thirds of the images, those that include 0, looks uniform, while the third third, those that does not include 0, seems to grow from the center, as new pixels can only be filled next to existing ones, and the only existing one at the begining is in the middle of the image.
See the code here
