For example, when an individual understands that the first letter of a CAPTCHA is an “a”, that individual also understands where the contours of that “a” are, and also where it melds with the contours of the next letter.Additionally, the human brain is capable of dynamic thinking based upon context.The team created puzzles by attempting to simulate what the manual claimed would cause bad OCR.The second team to claim inventorship of CAPTCHAs consists of Luis von Ahn, Manuel Blum, Nicholas J.Hopper, and John Langford, who first described CAPTCHAs in a 2003 publication and subsequently received much coverage in the popular press.Their notion of CAPTCHA covers any program that can distinguish humans from computers, including many different examples of CAPTCHAs.The first such people could be hackers, posting about sensitive topics to Internet forums they thought were being automatically monitored for keywords.To circumvent such filters, they would replace a word with look-alike characters.
This also means it will not be fooled by variations in letters.
While used mostly for security reasons, CAPTCHAs also serve as a benchmark task for artificial intelligence technologies.
According to an article by Ahn, Blum and Langford, “Any program that passes the tests generated by a CAPTCHA can be used to solve a hard unsolved AI problem.” They argue that the advantages of using hard AI problems as a means for security are twofold.
Such skills include, but are not limited to processing of sensory information such as identification of objects and letters within a noisy graphical environment"; and a 1998 patent by Lillibridge, Abadi, Bharat, and Broder,.
Both patents predate other publications by several years, though they do not use the term CAPTCHA, they describe the ideas in detail and precisely depict the graphical CAPTCHAs used in the Web today.