public function check()
 {
     $checkFailed = '';
     // get captcha string
     session_start();
     $captchaSolved = \ThinkopenAt\Captcha\Utility::checkCaptcha($this->gp[$this->formFieldName]);
     if (!$captchaSolved) {
         $checkFailed = $this->getCheckFailed();
     }
     return $checkFailed;
 }