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What is a CAPTCHA?

 , updated on April 03, 2016
A CAPTCHA, or Completely Automated Public Turing test to tell Computers and Humans Apart, is a challenge-response test for determining if a user is a human. It is used to prevent bots from accessing services intended for human use.
A variety of challenge techniques are used for CAPTCHA such as requiring users to type text from a distorted image or to select images that contain a particular item.
As the name implies, CAPTCHA were inspired by turing tests, a test for artificial intelligence whereby a bot on a chat can convince people they are chatting with a human. A CAPTCHA is a turing test in reverse whereby a person has to convince a computer that they are human.
Although CAPTCHA are automated on the service side, they require work on the part of users who typically deem them an annoyance. Some types of CAPTCHA are criticized for making services inaccessible to people with certain disabilities, including when an alternate challenge is available for people with visual impairments.
Overview: CAPTCHA
Robot Detection
A challenge-response test for determining if a user is a human.
Preventing bots from disrupting or abusing services intended for human use.
Cost in terms of user productivity.
Represents a barrier to people with certain disabilities.
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Artificial Intelligence

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Chinese Room
Decision Trees
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Event Processing
Forward Chaining
Fuzzy Logic
IT Biases
IT Examples
Machine Biases
Machine Unlearning
Predictive Analytics
Sentiment Analysis
Swarm Intelligence
Turing Test
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