An online forum is using chess puzzles as CAPTCHAs rather than the more traditional challenge-response tests which ask the user to identify distorted text.
The CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is a way for a website or online service to establish that a human has come calling rather than a piece of automated software. Typically a few visually distorted words are shown and punters have to type them into a dialogue box. Robots tend to be stumped by this verification process. The technology is often used to frustrate spambots from automatically signing up to web mail accounts and similar services.
The people behind online chess forum lichess.org have taken a different line by using a simple chess puzzle test instead. Although it's perfect for the forum in question the test is unlikely to go mainstream because it would completely fox anyone who had never played chess and not just the bots it wants to block.
And, as Graham Cluley of Sophos points out, computers have been better than humans (at below grandmaster level) at playing chess for many years.
At least the test isn't as obscure as a calculus-based CAPTCHA posited by eggheads at Croatia's Ruđer Bošković Institute a couple of years ago. ®