Gravatar(globally recognized avatar) is a service providing globally-unique avatars.
i-e It will show avatar( small icon like profile image) which will be displayed near the profile/user name in a blog/forum based on the email id used for creating the profile.
Once you create your Gravatar at http://en.gravatar.com/ for your email id, the gravatar will be automatically displayed in any gravatar supported blog/forum near your user name whenever you are adding any comment to the blog.
Wordpress is providing built-in support for gravatars as the gravatar is acquired by
Automattic which developed wordpress.
Content Management System (CMS) such as Drupal is providing support for Gravatar.
You can refer below url for implementing Gravator support in your website.