Simple and Easy CAPTCHA. Protects WordPress forms against spam bots by using a picture based challenge enabling users to solve it quickly and easily
How to obtain Public Key, Private Key and ZoneId? - For activating efence, you need a Public Key, Private Key and ZoneId that has been configured for you. Logon to efence.engageclick.com and register yourself as a member. Then create a page in order to get your public key, private key and zoneId.
I installed the efence plugin but the captcha is still not visible on the pages? - Check whether the efence plugin is enabled and is configured for the page you are testing the captcha for. e.g. If you want the efence captcha to be visible on User Registration page, you should configure it on the efence configuration page. Also check whether the public_key, private_key and zone_ids are set correctly.
Please refer here.