Newly added to the Support F.A.Q.: How do I modify my photo/avatar that shows up with my comments? Visit gravatar.com and set up an account associated with the same e-mail address you’ve used as a member. Keep in mind, we can’t support issues with gravatar.com, but that’s how it’s done. If the e-mail addresses match, you should see an updated avatar after a few minutes.
Thanks to Chris for asking this.