server/recaptcha.html

<html>
  <head>
    <title>reCAPTCHA demo: Simple page</title>
    <script>
        window.recaptcha_cb = (token) =>{
            window.token = token
        }
        const submit = () => {
            data = {
                token: window.token,
                cap: 'white hair yellow eyes',
            }
            fetch('http://127.0.0.1:5000/anime_heads', {
                method: 'POST',
                body: JSON.stringify(data),
                headers: new Headers({
                    'Content-Type': 'application/json'
                })
            })
            .then(function(res) {
                console.log(res.text())
            })
            delete window.token
        }
    </script>
    <script src="https://www.google.com/recaptcha/api.js" async defer></script>
</script>
  </head>
  <body>
      <div class="g-recaptcha" data-sitekey="6Lcb_fUUAAAAADgVNuvS161lQDZKs8G62lnBYqLN" data-callback="recaptcha_cb"></div>
      </br>
      <button type="button" onclick="submit()">submit</button>
  </body>
</html>