When we sign up for services online, or log in to secure pages we are usually asked to provide a username and password. In order to disincentivise people writing software to sign up to things in bulk you are sometimes shown a picture of some letters which have been distorted in some way. This method of stopping fraudulent sign ups and spam is called a CAPTCHA.

CAPTCHA stands for Completely Automated Public Turing test to tell Computers and Humans Apart and is devised as a way of trying to ensure that the person signing up for a service or sending an enquiry via an online for is indeed a person and not an automated programme used by hackers.

Alan Turing (the T in CAPTCHA) was a pioneering British computer scientist why as well as working at Bletchley Park helping to crack the Enigma code, also devised a series of tests to determine whether tasks had been performed by a human or a computer.