Pimcore\Model\Asset\Image\Thumbnail::getChecksum PHP Method

    public function getChecksum($type = "md5")
    {
        $file = $this->getFileSystemPath();
        if (is_file($file)) {
            if ($type == "md5") {
                return md5_file($file);
            } elseif ($type = "sha1") {
                return sha1_file($file);
            } else {
                throw new \Exception("hashing algorithm '" . $type . "' isn't supported");
            }
        }
        return null;
    }