Comment by Qub3d

There is a really interesting ongoing project to find the seed used for the default world and server icons:

Part 1: https://www.youtube.com/watch?v=lbR8ZY1Nsm8

Part 2: https://www.youtube.com/watch?v=eC7f9tMslVE

Part 2 covers most of the efforts to reverse-engineer the seed.