This option allows you to include a google reCaptcha validation at login. This means in addition to providing a valid usernane and password, you will also have to pass the reCaptcha test. Please note that enabling this option results in the zoneminder login page reach out to google servers for captcha validation. Also please note that enabling this option will break 3rd party clients like zmNinja and zmView as they also need to login to ZoneMinder and they will fail the reCaptcha test.