Completely Automated Public Turing Test to Tell Computers and Humans Apart (CAPTCHA) is a type of challenge-response test that is used to differentiate humans from automated bots or computers. CAPTCHAs are a widely used form of security measure to protect websites and applications from spammers and other automated malicious activities such as account takeover.
CAPTCHAs are typically implemented either as a graphical image (e.g. a sequence of random numbers and letters) or an audio file which must be correctly recognized by a human user before access is granted. CAPTCHAs are not intended for ordinary users and are usually only encountered by those attempting to bypass security measures.
The concept of CAPTCHAs was developed by Luis von Ahn, Manuel Blum, Nicholas J. Hopper and John Langford at Carnegie Mellon University in 2000. They proposed the use of CAPTCHAs to help digitize text which had been captured from old books and newspapers. CAPTCHA technology is now used by many large websites such as Google, Microsoft, and Yahoo! as an effective way to protect user accounts from automated attacks or abuse.
CAPTCHAs are also used in many employment-centric processes such as verification of resumes and job applications, verification of online polls and other surveys, and in online banking security measures. In some cases, CAPTCHAs are used in conjunction with other security methods such as fingerprint scanning and voice recognition.
Since CAPTCHA technology is widely used, there is an ongoing effort to find ways to bypass the human verification step. As technology advances, the security measures used in CAPTCHAs are improved—for example, using randomly generated images and audio files that are difficult for computers to recognize.
Overall, CAPTCHAs are an effective way to differentiate between humans and automated bots or computers, and provide greater security for websites and applications.
