Thanks to Tormod, I have now enabled Gravatars in the comments on my blog.
In short, a Gravatar is a small image that is associated with your email-address, and is then accessible through a certain URL-format. This way, when you sign a comment in my blog, or any other blog that has implemented Gravatars, your image will automatically be fetched from the gravatar.com server.
Check out their homepage for more info about how to create your own account and gravatar, and how to implement it on your own blog.
Go gravatars!
Go indeed