Many Wordpress blogs support the use of Gravatars, or, “globally-recognized avatars,” which link an image file to a user’s email address.
If you are working on a blog with native support for Gravatars, or you have activated the WP-Gravatar plugin, you can allow users on your blog to display their Gravatars when they leave a comment on a post.
You can go to Gravatar.com to set up a free account, which will link an image of your choice to one or many email addresses
This is a great way to add some easy customization and personalization to your blogging.