UPDATE: The combination tag captcha and tag recaptcha is not in use at present.
Very similar in concept to Tags [gmail] and [email] – married or single? which does not so far have an Answer to serve as a guide.
captcha without recaptcha 2 Open Qs, 1 follower, no Usage guide.
recaptcha without captcha 3 Open Qs, 0 follower, Usage guide:
For questions specifically about the reCAPTCHA service by Google.
captcharecaptcha 1 Open Q: Why is ReCaptcha sometimes really easy and sometimes really hard?
When should the above both be applied to a Q rather than one or the other?