public static function getGravatar(
        $email, $size = 80, $default = 'mm', $maxRating = 'g'
    )
    {
        $url = 'http://www.gravatar.com/avatar/';
        $url .= md5(strtolower(trim($email)));
        $url .= "?s=$size&d=$default&r=$maxRating";

        return $url;
    }