I didn't know I did until today but I hate this bloody thing. Even if you don't it you probably hate it too.
What is it? It is "Completely Automated Public Turing test to tell Computers and Humans Apart" and was invented at Carnegie Mellon University in 2000 by people who ought to be doing proper academic work involving the creation and dissemination of knowledge and not imposing such atrocities on the world. You hate their vile invention - I am sure you do.
Captcha is a computer program. It generates those invented words scrawled, in the fashion of a demented spider walking through ink, that are lie uneasily between legibility and illegibilty and which you supposed to be able to read and type into a box to prove that you are human. I usually have to have two or three attempts at different words before, possibly by chance, stumbling across the version that allows me to proceed. They might as well set one of Highlanders impossible quizzes with the wrong answers or ask in which Scottish league Rangers FC play. That would be less likely to cause apoplectic reactions.
At last one company has decided to abandon this abomination for which I commend it (although not for anything else). Let's hope it becomes a trend and then an accomplished eradication.
http://www.bbc.co.uk/news/technology-21260007