Implement the new google reCAPTCHA in PHP applications

reCaptcha.php

<?php
// reCAPTCHA 
// https://www.google.com/recaptcha/intro/index.html

    if (isset($_POST['g-recaptcha-response']) && filter_var($_SERVER['REMOTE_ADDR'], FILTER_VALIDATE_IP)) {
        $captcha = json_decode(file_get_contents('https://www.google.com/recaptcha/api/siteverify?secret=your_secret_key&response=' . $_POST['g-recaptcha-response'] . '&remoteip=' . $_SERVER['REMOTE_ADDR']), TRUE);
        if (isset($captcha['success']) && $captcha['success'] === TRUE) {
          //Captcha OK
        } else {
          //Captcha Error
          //Stop Script
        }
    } else {
      //Error, not valid parameters
      //Stop script
    }