Add reCaptcha to registration form

Just visit the reCaptcha website and sign in using your google account. Click on Create (+ icon) and you will see the form like the following.

Just enter your domain name instead of "example.com", select other options as shown above and click on submit. You will get Secret Key and Site Key as shown below.

Now, you can add reCaptcha to registration form by adding your Site key and Secret key in your "config.php" file as shown below.

define('RECAPTCHA_SECRET_KEY', 'Your reCaptcha Secret Key');

define('RECAPTCHA_SITE_KEY', 'Your reCaptcha Site Key');