By asking visitors to correctly say which direction of say, four (up, down, left or right) a part of a captcha appears to be "moving", it filters out the bots while allowing humans with optical illusion fooled eyeballs to pass the test. Given 16 of those captcha requests in a row and given that there are 2^2 choices per captcha, there is a 2^16*2 - 1 possible ways to enter 16 captchas wrong, but only 1 way to enter them right, leading to a filtration failure of around 1 in 4 billion.

Also, multiple captchas can be done in a row for each failure, but once say, 16 captchas have been solved in a row, access is granted for say, a month, until the captcha has to be done again.

It just feels like Hacker News is full of bots and I have a solution to this.