您可以使用过滤器get_avatar. 这个$avatar 价值类似于:
<img alt=\'\' 
    src=\'http://0.gravatar.com/avatar/04ef?s=32&d=http%3A%2F%2F0.gravatar.com%2Favatar%2Fad516%3D32&r=G\' 
    class=\'avatar avatar-32 photo\' height=\'32\' width=\'32\' />
 The
DOMDocument 看起来很复杂,但是
stuff done.
add_filter( \'get_avatar\', \'avatar_wpse_119123\', 15, 5 );
function avatar_wpse_119123( $avatar, $id_or_email, $size, $default, $alt )
{
    $doc = new DOMDocument;
    $doc->loadHTML( $avatar );
    $imgs = $doc->getElementsByTagName(\'img\');
    if ( $imgs->length > 0 ) 
    {
        $url = urldecode( $imgs->item(0)->getAttribute(\'src\') );
        $url2 = explode( \'?\', $url ); // roughly, the first part is the avatar, the second is the default avatar
        $avatar= "<img src=\'$url2[0]?s=30\' alt=\'\' class=\'avatar avatar-30 photo\' height=\'30\' width=\'30\' />";
    }
    return $avatar;
}
 唯一的问题是,这不会影响管理栏用户的菜单。