Registration Pro is fully integrated with Google reCaptcha, so you don't have to worry about spam registrations on your site.
Getting a Google API Key
To gain access to this page you’ll need to be logged into a Google account. You’ll be asked to register your website, so give it a suitable name, then list domains (for example smith-consulting.com) where this particular reCAPTCHA will be used. Subdomains (such as test.smith-consulting.com and staging.smith-consulting.com) are automatically taken into account.
With that done you’ll be given a site key and its partner secret key:
Adding to Registration Pro
navigate to the page where you have added the Registration module and select Templates from the Admin Menu.
You will see your form builder, similar to the one pictured below.
Expand the Other Controls section of the template editor and select reCaptcha.
You can drag this onto your form where you would like it to appear. Once you place the control, you will receive a popup prompt to apply your site key and secret key from Step 1 above:
Enter your Google keys and click Update. Once you have finished configuring your form, be sure to save the template.
The reCaptcha will now display on your form"