Captcha definition
Examples of Captcha in a sentence
When creating user profiles, Captcha is used to prevent access to robots.
Observe that we do not assume anything about the non- malleability of the Captcha puzzles, i.e. it may be possible for the adversary that knows some puzzle z = G(x) to produce (without decoding x) a puzzle that zj such that H(zj) is in some way related to x.
This corresponds to the real-life situation, where the Captcha puzzles are indeed malleable (for example, removing the first letter from a graphical representation of a text may be easy, even if the whole text is unreadable — consider e.g. the image on Fig.
Both designing and breaking Captcha schemes is subject of intensive and active research.
When Google bought Captcha, an anti-bot security system, in 2009 it found that it could use the requirements of humans to pass an online Turing test (the ‘I am not a robot’ security programme) to test its own ▇▇▇ DeepMind (86).