public function isValid($value, $context = null) {
        $frontController = \Zend_Controller_Front::getInstance();
        $request = $frontController->getRequest();
        $value = $request->getParam('g-recaptcha-response');
        if (empty($value)) {
            $this->_error(self::CAPTCHA_EMPTY);
            return false;
        }
        $this->_value = $value;

        if (!$this->_verify($value)) {
            $this->_error(self::INVALID_CAPTCHA);
            return false;
        }

        return true;
    }