Captcha is an acronym of Completely Automated Public Turing Test to Tell Computers and Humans Apart.

What is a Captcha?

Captcha is an acronym of Completely Automated Public Turing Test to Tell Computers and Humans Apart. The most popular version distorts letters and numbers and asks users to interpret and reproduce these characters.


How did they come about and what are they for?

The term was coined by researchers at Carnegie Mellon University in Pittsburgh to describe programs that verify that a person and not a computer is entering data. Captchas were rapidly adopted across the Internet and are commonly used now on online forms, to help prevent spam and the automatic extraction of data from websites.

By enabling websites to detect non-human interaction, they can successfully prevent the activity of bots. The problem however is that early versions of captchas were cumbersome and impractical from a user's point of view.


Who uses captchas

Captchas are used on many websites that need to check that a user is not a robot. They are often used to ensure the veracity of online surveys, to prevent the risk of automated voting.

They are also frequently used in registration forms, especially where users can create free accounts. Captchas prevent spammers from using bots to create massive amounts of email addresses to use for spam.

Ticketing websites have also taken advantage of this technology to prevent touts from buying up tickets for major events and selling them for much higher prices. Finally, Web pages and blogs with areas for comments and contact forms use them to prevent spam or bots.

Unfortunately, as technology and hackers become more sophisticated, so do their tactics. Although captchas are secure in general, some cyber-criminals have started to use them in fake or fraudulent websites to make the site more believable.


The future of the captcha

In 2013, the startup Vicarious claimed that it had managed to find a way around captchas thanks to an artificial intelligence system. Over four years later they revealed the methodology used in ‘Science’. In the last few years, as AI improves, more people are finding ways around captchas.

Audio captchas for example, where the words needed to identify the person are read out loud, ceased to be used in 2011 by companies such as Microsoft, Digg or eBay, when IT experts at Stanford managed to decrypt them.

In 2014, Google officially stopped using text-based captchas, replacing them with the button ‘I am not a robot’. This AI system includes a second test where users have to click all the images that contain a certain object. The system is called reCaptcha.

At the end of 2016, the company announced the Invisible reCaptcha which uses Advanced Risk Analysis. This is a model that uses AI to look for indications of human behavior and runs in the background detecting mouse movements.

As the world becomes increasingly dependent on smartphones, some developers are working on new versions of captchas, specifically for mobile devices. Amazon, for example, has patented a captcha system that humans are sure to fail. The creators have explained that humans do not have the ability to pass certain basic logic tests that machines can rapidly identify.