Gravatars
From MoodleDocs
Gravatar (an abbreviation for globally recognized avatar) is a service for providing globally unique avatars.
An administrator can enable the use of gravatars in Settings > Site administration > Users > Permissions > User policies. If a user has not uploaded a user picture, Moodle will check whether the user's email address has an associated gravatar and if so, will use the gravatar as the user's picture.
Use your Gravatar in Moodle 2.2 screencast:
<mediaplayer>http://www.youtube.com/watch?v=Z4b7tJedlMA</mediaplayer>