This site uses Gravatars to handle your avatar.
I see a good number of you already use the service and your avatar has carried over automatically. For those that are unfamiliar with it, a Gravatar, or globally recognized avatar, is an avatar image that follows you from website to website, appearing beside your name when you comment on any Gravatar enabled sites. Many sites are now supporting Gravatars, so it is worth creating an account. Signing up for a http://www.gravatar.com account is FREE, and all that’s required is your email address. Once you’ve signed up you can upload your avatar image and soon after you’ll start seeing it on Gravatar enabled sites such as this one.