One of the only changes you should notice since I upgraded Fretnoise.com to WordPress 2.7 is the weird icon thingies next to your comments. These are called “Gravatars”, which comes from “Globally Recognised Avatars”. Basically, if you go and register at gravatar.com then whenever you use your email address whilst commenting on a Gravatar-enabled blog then your chosen picture will appear next to your comment. If you don’t register with gravatar.com, then you get a nice interpretation of your email address / IP address in the form of a little pattern (called an “Identicon”) instead.

The important thing to note is that although the image is retrieved (if you’ve signed up) or generated (if you haven’t) based on your email or IP address, those private bits of information don’t appear on this site. The images are retrieved (or generated) based on a one-way hash of your address which, by its nature, is very very difficult to reverse. For example, my gravatar image is requested via the following url:

http://www.gravatar.com/avatar/4e84e74a1cba73457b2d3d83e2034f38?d=identicon
(note that my email address isn’t in that url)

The Identicons for non-registered commenters are requested from the same place, but with a different unique identifier, like this :

http://www.gravatar.com/avatar/12341234123412341234123412341234?d=identicon

I hope that clears that up

Here’s another (somewhat more geeky) explanation.