What is the system that allows for anonymous pictures portraits?

Question

Anyone knows what is the system that allow blogs / websites to generate a random picture for anonymous commenters? Its always the same picture if you input the same name and email, seems very useful but can't track down what it is.

It's used here on stackoverflow, and I've seen it on a number of other sites and blogs.

Thanks!

Answer 1

Gravatar

Answer 2

Identicon is what I was really looking for, but the Gravatar answer allowed me to find it! Thanks Jeff! I assume the lazy registration is handled separately then.

See: http://scott.sherrillmix.com/blog/blogger/wp_identicon/