Honestly, I write it captcha most of the time. Properly stylized CAPTCHA, this machine-defeating checking mechanism (created in 2000, named in 2003) seems like a portmanteau of "capture" and "gotcha", alluding to its identification of bots online. While that was indeed a major influence on the development of the word, CAPTCHA is actually a loose acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart", a Turing Test being a way of telling apart humans and robots. Obviously the acronym is a bit messed up and fitted to look how the creators wanted it to; if it conformed to standards of capitalization, the CAPTCHA should actually be a CAPTTTCHA. When Google invented a CAPTCHA system in 2007 to simultaneously digitize books and check for bots, they named it the reCAPTCHA, which makes the CAPTCHA a word so old that it is already the etymon of another.
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd