An identicon is a generated avatar using the hash (a "unique" number created based on data, in this case your username) and using that number to decide the design. The hash becomes a 32-bit integer, the first 8 bits decide the shape and design, while the rest decide the color, each section of 8 bits corresponding for red, green and blue values. The shape uses custom designs based on 4 sections of bits, while the pixel draws a pixel on a bit that is on (pixel is much better with a 64-bit number) Also includes Drawing API because managing points is too tedious
I was curious about how Github and Stack Exchange created default avatars, so I explored the web.