Captcha: What is it and what does it mean?

Likely every Internet user has encountered captchas. With these, websites namely like to check whether the visitor is actually a human being. We explain what the term actually means.

Access control: Captchas are also based in name on the idea of the Turing test.

The number of bots on the Internet is constantly increasing. To prevent these from gaining access, captchas are used on many sites, as already explained here.

Captcha: What is it and what role does the Turing test play?

But what is actually behind the term is not known to most people.

• Captcha stands for "Completely Automated Public Turing Test to tell Computers and Humans Apart", with the initial capital letters making up the word.
• In terms of content, the mention of the Turing test is particularly interesting: this was developed in 1950 as a thought experiment by the English physicist Alan Turing to determine whether a user is a human or a computer. After all, this is exactly the purpose of captchas.
• As bots got better and better over time and were able to solve simple captchas, captchas also had to become continuously more sophisticated.
• So there are now several common types of tasks that visitors have to solve. Picture puzzles are just as common as number games or completing graphics by moving missing parts.

In all cases, the task is always randomly generated. Captchas are thus fully automated, so that page operators only have to perform the integration.