Captcha

This is an acronym for Completely Automated Public Turing test to tell Computers And Humans Apart. When you comment on this blog, you meet a captcha which you copy. Captchas are the seemingly useless letters and numbers used to prevent automated software from spamming the website. A captcha has an algorithm to show different new challenges which requires real human intelligence to solve. They are supposed to be random but sometimes randomness can be funny or bad: