How does this checkbox recaptcha work and how can I use it?

Question

I\'ve recently signed up to the oneplusone website https://account.oneplus.net/sign-up, and noticed this checkbox recaptcha

How does it work, and how can I

Answer 1

Here is my code running without problem in PHP:

Client Side:

Server Side:

if (isset($_POST['g-recaptcha-response'])) {
    $captcha = $_POST['g-recaptcha-response'];
    $privatekey = "SECRET_KEY";
    $url = 'https://www.google.com/recaptcha/api/siteverify';
    $data = array(
        'secret' => $privatekey,
        'response' => $captcha,
        'remoteip' => $_SERVER['REMOTE_ADDR']
    );

    $curlConfig = array(
        CURLOPT_URL => $url,
        CURLOPT_POST => true,
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_POSTFIELDS => $data
    );

    $ch = curl_init();
    curl_setopt_array($ch, $curlConfig);
    $response = curl_exec($ch);
    curl_close($ch);
}

$jsonResponse = json_decode($response);

if ($jsonResponse->success == "true")
    doSomething();
else
    doSomeOtherThing();

:)