Включите скрипт в HTML
<script type="text/javascript" src="/path/to/script.js"></script>
Batman
<script type="text/javascript" src="/path/to/script.js"></script><html>
<head>
<title>reCAPTCHA demo: Simple page</title>
<script src="https://www.google.com/recaptcha/api.js" async defer></script>
</head>
<body>
<form action="?" method="POST">
<div class="g-recaptcha" data-sitekey="your_site_key"></div>
<br/>
<input type="submit" value="Submit">
</form>
</body>
</html>