A Gravatar is a picture that follows you around from site to site. If you check out a post that has comments you’ll see that some have pictures next to their name and some don’t. Those that don’t, don’t have a gravatar.
Getting your own Gravatar is easy. Open a free account with Gravatar and upload your picture or logo.
If you don’t get how it works watch the video on the front page, it explains it really well.
Now when you’re leaving comments you’re also leaving a little picture of your logo everywhere you go.