Random avatar generator

Question

Possible Duplicates:
what is the algorithm used to generate those little gravatar identicon images?

StackOverflow seems to have nice, randomly generated avatars for default users. How do I do that (preferably with PHP)?

Answer 1

http://en.gravatar.com/

Answer 2

Gravatar: http://en.gravatar.com/

Here is a link to their reference php implementation: http://en.gravatar.com/site/implement/php