public function stringify($server, $secret, $original, $commands)
{
if (count($commands) > 0) {
$commandPath = implode('/', $commands);
$imgPath = sprintf('%s/%s', $commandPath, $original);
} else {
$imgPath = $original;
}
$signature = $secret ? self::sign($imgPath, $secret) : 'unsafe';
return sprintf('%s/%s/%s', $server, $signature, $imgPath);
}