Include reCAPTCHA on the form

reCAPTCHA is added by including the JavaScript from Google somewhere. For ASP.NET Core add it to the Scripts section:

@section Scripts {
<script src="https://www.google.com/recaptcha/api.js" async defer></script>
<partial name="_ValidationScriptsPartial" />
</script>

Next, you will need to tell reCAPTCHA where to put the CAPTCHA control. Paste the following markup inside the form element:

<div class="form-group">
<div class="g-recaptcha" data-sitekey="SITE_KEY"></div>
</div>

For the data-sitekey attribute, use the reCAPTCHA site key from the site settings.