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Is there a DECAPTCHA library in .NET?

I am looking for some sample projects for reading CAPTCHA images. Is it in C # or VB?

pseudo code:

String captchaText = CaptchaDecoder(Image captchaImage);
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c # captcha decode
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3 answers

There are so many types of Captchas that you will not find a single library to read all of them. If you are only interested in one type, you may have more luck. Even then, Captchas have many variations, and engines often produce (whether intentionally or accidentally) tricky that even people cannot understand. People can click a small icon to get a new one; your program may not be able to.

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Take a look at:

Strengths and weaknesses of text-based CAPTCHA. ACM Computer and Communication security 2011 (CSS2011). link

Authors Introduce CAPTCHA Switch and Explain Common CAPTCHA Hacking Algorithm

In this section, we present our interceptor, Decaptcha, which can break many popular captchas, including eBay, Wikipedia and Digg [...] Decaptcha implements an updated version of the three-stage approach in 15,000 lines of code in C # [...]

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This is easier said than done.

This includes either forcing transcoding or using OCR algorithms to try and discover what is written in captcha.

You might want to check out this related question: Has reCRaptcha / OCR'd / defeated / broken been hacked / hacked?

It also depends on what methods were used to create the CAPTCHA. Some distort text, and some compress text.

Your question is a bit vague.

Further reading here: http://en.wikipedia.org/wiki/CAPTCHA

  • Christian
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