recaptcha.php

<?php

define('RECAPTCHA_PUBLIC_KEY', '');
define('RECAPTCHA_PRIVATE_KEY', '');

// Formulaire
<script src="https://www.google.com/recaptcha/api.js"></script>
<div class="g-recaptcha" data-sitekey="<?php echo RECAPTCHA_PUBLIC_KEY; ?>"></div>

// Validation du post
function checkRecaptcha()
{
	if (isset($_POST['g-recaptcha-response'])) {
		$recaptcha_response = urlencode($_POST['g-recaptcha-response']);
		$private_key = urlencode(RECAPTCHA_PRIVATE_KEY);
		$ip_address = urlencode(getRemoteIP());
		$response = file_get_contents("https://www.google.com/recaptcha/api/siteverify?secret={$private_key}&response={$recaptcha_response}&remoteip={$ip_address}");
		$result = json_decode($response);
		if (is_object($result) && isset($result->success))
			return $result->success;
		return false;
	}
	return true;
}

function getRemoteIP()
{
	if (!empty($_SERVER['HTTP_CLIENT_IP']))
		$ip = $_SERVER['HTTP_CLIENT_IP'];
	elseif (!empty($_SERVER['HTTP_X_FORWARDED_FOR']))
		$ip = $_SERVER['HTTP_X_FORWARDED_FOR'];
	else
		$ip = $_SERVER['REMOTE_ADDR'];
	return $ip;
}