What is Captcha? Learn about the bot-protection programme

If you’ve ever purchased something online there's a good chance you’d have used CAPTCHA. Find out more about what it is.

If you’ve ever purchased something online and been required to type in a random string of distorted text prior to doing so, it’s likely you’d have used CAPTCHA. But what more do you need to know about this clever automated computer program?

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What is CAPTCHA?

CAPTCHA is a computer program that is designed to protect websites against Bots by automatically telling humans and computers apart. The program is commonly used across the internet, particularly when purchasing products online. 

What does CAPTCHA mean?

CAPTCHA stands for: Completely Automated Public Turing test to tell Computers and Humans Apart.

Captcha example on computer screen

How does CAPTCHA work?

It works on the basis that human users can read distorted letters or numbers while computers can’t. CAPTCHA generates and grades tests that humans can pass but which are impossible for computer programs to solve.

Who invented it?

According to a US patent application filed in 1997, two groups working in parallel invented the most common CAPTCHA. Eran Reshef, Gili Raanan and Eilon Solan formed one group, while the other was made up of computer scientists Mark D. Lillibridge, Martín Abadi, Krishna Bharat, and Andrei Broder.

However, the actual term CAPTCHA is believed to have originated three years later, in 2000, from a four-man team at the Carnegie Mellon University – Luis von Ahn, Manuel Blum, Nicholas Hopper and John Langford. This team were the creators of reCAPTCHA, a Captcha-like system bought by Google in 2009.

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