What is a Gravatar?
Gravatars are Globally Recognized Avatars. An avatar or gravatar is an icon, or representation, of a user in a shared virtual reality, such as a forum, chat, website, or any other form of online community in which the user(s) wish to have something to distinguish themselves from other users. All WordPress blogs use them and will show one automatically based on the email you enter in your comment on a blog. It’s a great way to set this up once and see it anywhere you might comment, including our Core community blog.
How Gravatar works
You create an account with Gravatar using any email address and upload a photo/image to the account. Whenever you comment on a blog post using the email address registered with Gravatar, the image you uploaded at Gravatar is visible next to the comment. So go to http://en.gravatar.com/ to get started!