recaptcha demo

<html>
  <!-- SOURCE: https://developers.google.com/recaptcha/docs/display -->
  <head>
    <title>reCAPTCHA demo</title>
    <script type="text/javascript">
      var verifyCallback = function(response) {
        document.getElementById('captcha').value = response;
      };
      var onloadCallback = function() {
        grecaptcha.render('placeholder', {
          sitekey : '6Ld15D8UAAAAAKCBnh_NrSaoqYmhOIfx0uyJUtzC',
          callback : verifyCallback,
          size: 'invisible',
          'expired-callback': function () {
            verifyCallback('');
          }
        });
        grecaptcha.execute();
      };
    </script>
  </head>
  <body>
      <input type="text" name="captcha" id="captcha">
    <script src="https://www.google.com/recaptcha/api.js?onload=onloadCallback&render=explicit" async defer></script>
  </body>
</html>