We are still actively working on the spam issue.
reCAPTCHA is a service run by Google to both help digitise books, and prevent bots from spamming. It is used on 4chan to prevent bots from spamming posts or reports.
reCAPTCHA is not a silver bullet. Any sufficiently dedicated spammer can just hire some people from a poor country to fill out CAPTCHA problems for a few cents each. That being said, it's reasonably effective on most websites.
How it works
- The user's browser requests a challenge (an image with distorted text) from reCAPTCHA. reCAPTCHA gives the user a challenge and a token that identifies the challenge.
- The user fills out the web page form, and submits the result to your application server, along with the challenge token.
- reCAPTCHA checks the user's answer, and gives you back a response.
- If true, generally you will allow the user access to some service or information. E.g. allow them to comment on a forum, register for a wiki, or get access to an email address. If false, you can allow the user to try again.
It was discovered by some anon on /g/ that the CAPTCHA challenge becomes more difficult if you log out of your Google account.