It's a hashcash: https://wehatecaptchas.com/load.php?name=captcha-worker.js https://wehatecaptchas.com/load.php?name=captcha-worker.js Proof of work is trivia

It's a hashcash: https://wehatecaptchas.com/load.php?name=captcha-worker.js https://wehatecaptchas.com/load.php?name=captcha-worker.js Proof of work is trivially parallelizable, and 2^(5*4)=1048576 options are super easy to go through for spammers.