if($response->isError()){
    $result = $response->getMessage();
}
else{
    $result = 'true';
}

if($response->isError()){
    $result = false;
}
else{
    $result = true;
}

&preHooks=`modcaptcha.preHook` 
&captcha_key=`mycaptcha` 

<input type="text" name="mycaptcha">
[[!$modcaptcha? &captcha_key=`mycaptcha`]]

$code = $this->getProperty('code');

$code = $this->modx->request->parameters[$this->getProperty('method')][$key];