0 a system that is used to make sure that a human being, not a machine, is using a computer. The person may be asked to type in a series of letters or numbers, or to complete a simple game. The word captcha is made up of the first letters of words in the phrase Completely Automated Public Turing test to tell Computers and Humans Apart:
The leading ticket sales website is to stop using the human verification system captcha in favour of something more user-friendly.
Some incorporate the use of captcha to ensure user interaction.
A human brain can read captcha letters in seconds, however, even a supercomputer can not do that in a finite time.
Commonly, captchas are dynamically created images of random numbers and/or letters.
Also, many implementations of captchas (particularly ones desired to counter circumvention) are inaccessible to humans with disabilities, and/or are difficult for humans to pass.
The use of captchas is controversial.
Captchas are used by freemail services to prevent automatic creation of a huge number of email accounts and to protect automatic form submissions on blogs, forums and article directories.
A captcha is a challenge-response test frequently used by internet services in order to verify that the user is actually a human rather than a computer program.
