public static function get_gravatar($email, $size = 32)
    {
        if (self::is_https()) {
            $url = 'https://secure.gravatar.com/';
        } else {
            $url = 'http://www.gravatar.com/';
        }

        $url .= 'avatar/' . md5($email) . '?s=' . (int) abs($size);

        return $url;
    }