This tutorial is for Form Tools 3 only. Google deprecated the old reCAPTCHA v1 method which was used by Form Tools 2.
If you find your form has become subject to spammers, adding a CAPTCHA is a standard way to cut down on spam. CAPTCHA is an acronym for Completely Automated Public Turing test to tell Computers and Humans Apart. There are many types of CAPTCHA out there. The Form Tools API provides an easy integration with reCAPTCHA V2 - a Google service - that shows an "I'm not a robot" checkbox in your form that users must click in order to submit the form.
Please note, this only works for forms that are found on the same website as your Form Tools installation.