I made a simple form using the newest reCaptcha but I don't know how to block sending a form if captcha was wrong rewritten.
<!DOCTYPE html>
<html>
<head>
<title>reCaptcha</title>
<script src='https://www.google.com/recaptcha/api.js'></script>
</head>
<body>
<form action="validate.php" method="POST">
<div class="g-recaptcha" data-sitekey="My public key"></div>
<input type="submit" value="Submit Form" style="width:100px;height:20px">
</form>
</body>
</html>
</!DOCTYPE>
</div>