Recaptcha for register form can be enabled or disabled from Theme Options – Advanced – Recaptcha settings;
The code is taken from https://www.google.com/recaptcha/intro/index.html
If enabled – the register form looks like this:
Recaptcha requires you add your own Site Key and Secret Key.
Click on Get Recaptcha
Register your site info:
Get the site key and secret key
Copy/paste in theme options