This plugin used to make gravatars load twice bigger images than requested by themes and plugins for crispier display on retina screens.
WordPress 4.4, however, adds this functionality, so the plugin is no longer needed, thus deprecated.
You should most probably deactivate and delete it.
Simply download and activate it. No additional setup is required.
1.1.2
Deprecation in favor of built-in image retina support in WordPress 4.4
1.1.1
Tested against WordPress 3.9
1.1
- update for better support for avatars with default value
1.0
The plugin was released.