CAPTCHA can be enabled to deter automated form submissions.
To enable CAPTCHA:
Click the form’s Options button () and select Settings.
Switch the Require CAPTCHA toggle to the right.
Form submissions now require the completion of a CAPTCHA check.
By default, Liferay uses a “Simple CAPTCHA” check. This can be configured and changed to use an alternative CAPTCHA engine, like Google’s reCAPTCHA service. For more information on how to do this, see Authentication Basics.