15-10-2010, 09:17 AM
CAPTCHA and HIP
What is CAPTCHA and what is HIP?
When you try to access some web sites you may be asked to type in what you see in a picture. If you can read the picture the web site assumes you are human because computers (in this case bots sent by spammers) cannot read such text. The word CAPTCH is an acronym and stands for
Completely
Automated
Public
Turing test to tell
Computers and
Humans
Apart
In order to "read," computers must do Optical Character Recognition (OCR), a process that starts with the pixels of an image and ends by identifying letters. OCR works by first separating the foreground (letter) color from the backround color, then collecting pixels with the letter color into groups so that each group corresponds to a letter, and then trying to figure out the shape of the letter. By 1990 people had written programs that could perfrom these tasks well for some types of text and there are several products in the market that do a good job with printed text using the Roman (or other western) alphabet. (Ironically, by the time the products reached the market the need for OCR had been greatly diminished because most text was entered through computers in the first place.)
CAPTCHA (initiated by researchers at Carnegie Mellon University and IBM in 2000) works by understanding the OCR methods and displaying text that can break them. Of course this a game two can play, so OCR designers can modify their methods to read the distorted text.
While CAPTCHAs started with text they have started using other images that maybe easy for a human to recognize but they baffle computers. Also, some of the new tests are not public so the technology is now called HIP that stands for
Human
Interaction
Proof
While it avoids the historical reference to Turing, it is a shorter acronym and easier to remember.
Alan Turing and the Turing Test
Alan Turing (1912-1954) is considered the inventor of the modern computer. He did both theoretical work and direct development for a computer that was able to break the ENIGMA German codes during World War II. You should read at least a Short Biography by Jerome M. O’Connor. More information can be found in the Wikipedia entry, and even more in a full Biographical page created by Andrew Hodges, author of the book Alan Turing: the enigma (Touchstone, 1983).
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