1. Go to User Manager > Options.
2. Change the Captcha field to Captacha-Recaptcha.
   
3. Click Save & Close.

Create reCAPTCHA key

1. To get a public and private key for your domain, go to http://google.com/recaptcha
2. Click on the link: USE reCAPTCHA ON YOUR SITE and Sign Up Now.
3. Enter your domain and click on Create Key.
4. You will now have a public and private key.

Enable ReCaptcha Plugin

1. Go to Extensions > Plug-ins.
2. Use the filter and search for Captcha - ReCaptcha.
3. Click on the plugin and make sure the status is set to Enabled.
4. Under Basic Options input the public and private keys.
5. Click on Save & Close.