/**
* By default WordPress shows the images from Gravatar.com on the comments and in the Dashboard.
* If your site doesn't use comments, you can disable the Gravatar in Settings > Discussion > Avatar Display
* But the user's Gravatar will still show in the top-right corner of the Dashboard.
* To disable that completely, we need to filter the get_avatar() function.
* From the Codex: The "get_avatar" filter can be used to alter the avatar image returned by the get_avatar() function.
*
* @source: codex.wordpress.org/Plugin_API/Filter_Reference/get_avatar
*/
add_filter( 'get_avatar', 'so_disable_gravatars', 10, 2 );
function so_disable_gravatars( $avatar ) {
$avatar = '';
return $avatar;
}