If you choose not to sign up with Gravatar, the default icon set by the Administrator appears next to your name.
Providing your users with avatars has become a convention in web-publishing.
When browsing different web sites, you may notice that many users have a picture next to their name.
These pictures are called "avatars." Word Press, however, uses a specific type of avatar called "Gravatars"--short for "Globally Recognized Avatar." Unlike standard avatars, Gravatars follow you around the web and automatically appear when you post a comment on a Word Press site.
Word Press integrates Gravatars into every Word Press site.
Once registered with Gravatar, the service matches your Word Press profile information to the email address registered with Gravatar and displays your custom Gravatar image next to comments and (optionally) elsewhere on the Word Press site.
allows you to customize how Word Press outputs your comments in your theme.
It also controls the size of the Gravatar attached to the comments.
By default, Gravatars are displayed at 32px x 32px.
To change the size of the Gravatar, you can use the ‘avatar_size’ argument with works slightly different.
The first argument you pass it must be a user's ID, email address or the comment object.
You can then specify the size of the returned Gravatar, the URL for the default image you want to display if a user does not have a Gravatar, and the alternate text for the Gravatar image.
This will return a 50px x 50px Gravatar: class, you would alter the style of both the Gravatar in your theme's comments and admin bar.