final static function getDriver(array $drivers=array('gd')) {
        foreach ($drivers as $driver) {
            if (!preg_match('/^[a-z0-9\_]+$/i', $driver))
                continue;
            $class = __NAMESPACE__ . "\\image_$driver";
            if (class_exists($class) && method_exists($class, "available")) {
                eval("\$avail = $class::available();");
                if ($avail) return $driver;
            }
        }
        return false;
    }