The term CAPTCHA is an acronym for completely automated public Turing test to tell computers and humans apart. This is a computer program designed to distinguish between a human user and a machine or a bot, typically as a security measure to prevent spam and data misuse. The concept of CAPTCHA was introduced as early as 1997, when the internet search company AltaVista was trying to block automatic URL submissions to the platform that were skewing their search engine algorithms. To tackle this problem, AltaVista's chief scientist, Andrei Broder, came up with an algorithm to randomly generate images of text that could easily be identified by humans, but not by bots. Later, in 2003, Luis von Ahn, Manuel Blum, Nicholas J Hopper, and John Langford perfected this technology and called it CAPTCHA. The most common form of CAPTCHA requires...
![country flag](/images/countries/us.png)
![country flag](/images/countries/gb.png)
![country flag](/images/countries/india.png)
![country flag](/images/countries/germany.png)
![country flag](/images/countries/france.png)
![country flag](/images/countries/canada.png)
![country flag](/images/countries/russia.png)
![country flag](/images/countries/spain.png)
![country flag](/images/countries/brazil.png)
![country flag](/images/countries/australia.png)
![country flag](/images/countries/singapore.png)
![country flag](/images/countries/hungary.png)
![country flag](/images/countries/ukraine.png)
![country flag](/images/countries/lux.png)
![country flag](/images/countries/estonia.png)
![country flag](/images/countries/lithuania.png)
![country flag](/images/countries/southkorea.png)
![country flag](/images/countries/turkey.png)
![country flag](/images/countries/switzerland.png)
![country flag](/images/countries/colombia.png)
![country flag](/images/countries/taiwan.png)
![country flag](/images/countries/chile.png)
![country flag](/images/countries/norway.png)
![country flag](/images/countries/ecuador.png)
![country flag](/images/countries/indonesia.png)
![country flag](/images/countries/newzealand.png)
![country flag](/images/countries/cyprus.png)
![country flag](/images/countries/denmark.png)
![country flag](/images/countries/finland.png)
![country flag](/images/countries/poland.png)
![country flag](/images/countries/malta.png)
![country flag](/images/countries/czech.png)
![country flag](/images/countries/austria.png)
![country flag](/images/countries/sweden.png)
![country flag](/images/countries/italy.png)
![country flag](/images/countries/egypt.png)
![country flag](/images/countries/belgium.png)
![country flag](/images/countries/portugal.png)
![country flag](/images/countries/slovenia.png)
![country flag](/images/countries/ireland.png)
![country flag](/images/countries/romania.png)
![country flag](/images/countries/greece.png)
![country flag](/images/countries/argentina.png)
![country flag](/images/countries/netherlands.png)
![country flag](https://cdn.packtpub.com/flag/004da5c4-583f-4e69-a0a8-0e999f350f90_128px-Flag_of_Bulgaria.png)
![country flag](/images/countries/latvia.png)
![country flag](/images/countries/southafrica.png)
![country flag](/images/countries/malaysia.png)
![country flag](/images/countries/japan.png)
![country flag](/images/countries/slovakia.png)
![country flag](/images/countries/philippines.png)
![country flag](/images/countries/mexico.png)
![country flag](/images/countries/thailand.png)