| Wednesday July 30th 2014

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How not to design a CAPTCHA


Sony captcha

Unfortunately Sony missed the entire point of a CAPTCHA. Instead of using an obfuscated image which is difficult for computers to recognize the characters, they include the CAPTCHA’s unobfuscated characters in HTML and use CSS and JavaScript to make the characters appear slightly distorted.

While taking a Digital Image and Video Processing class, I picked up a summer hobby of writing CAPTCHA breakers. Most CAPTCHAs can be decoded with a combination of Gaussian edge detection and XOR difference analysis with known characters. However this one falls to a simple regex.

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