Posted April 09, 2016
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Back in the 80-90's there was a technology called OCR which builds a library of characters from fonts, and then does it's best to match everything. Unfortunately you'd get 80% good and static or glitches in areas would get things wrong. Mind you it was probably good enough for people who are blind since redundancy in language is high enough you can usually figure out what's wrong.
Anyways, a lot of Captcha today is warping the text or adding static or doing things that makes it harder if not impossible to do identification. Unfortunately a large portion of the time the images are so warped i can't figure it out either, making the natural organ we have in our heads for visually figuring things out pointless if things are swirled and warped and inverted and strikes through it and you can't tell if the random letters are an i, l, 1, or any other number of odd combinations that you effectively just blitz through to find a good easy captcha because they are crap.
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It's a clever idea. You provide a service that benefits other people and in turn you get a large number of free workers.