Okay, some of the functions of WordPress are a bit counterintuitive. Some of you, who want to comment, ask yourselves “where the hell can I set my avatar for WordPress account” – well, it’s not that easy. Here’s how to do it though, courtesy of Edard:
You’ll need to sign up at http://www.gravatar.com with the email address that you’ve associated in your blog with your admin user account, and upload you image to gravatar.com. After you’ve done that your gravatar.com image will appear whenever you post on your own blog or on other WordPress blogs (if you put that email address into the mail field of the comment form at that other blog).