This plugins shows Gravatar avatars instead of the generic user image.
Install the plugin on a Jenkins instance running at least 1.434, and it will automatically show Gravatars for the users that has an email and a Gravatar. No configuration except installing the plugin.
The plugin will re-check every 30 minutes to see if any user has configured a gravatar. So if you have configured a gravatar and it does not show up, please wait at least 30 minutes before thinking its a bug.