Is there any DECAPTCHA library in .NET?

Question

I'm looking for some sample projects to read CAPTCHA images. Is there any in C# or VB ?

pseudo code:

String captchaText = CaptchaDecoder(Image captchaImage);

Doesn't this defeat the purpose of CAPTCHA in the first place? — Corey, Dec 02 '10 at 02:29
Oh Wait, you want to use a CAPTCHA system or "defeat" the CAPTCHA system? — Tivie, Dec 02 '10 at 02:33
Could there be *any* valid reason to have such a tool, and why would any sane person here want to help you produce more spam? — Remus Rusanu, Dec 02 '10 at 02:38
@Remus: Share it with us man, we promise use it for charity projects. — Xaqron, Dec 27 '10 at 17:06
@RemusRusanu: can you give us *any* valid reason as to how can any sane person declare bypassing captchas programmatically is not one of them ? — Veverke, Sep 09 '15 at 13:48
@RemusRusanu: I'll give you a reason: scraping web pages that have captchas on them. And yes, there are legitimate purposes for doing that. — Robert Harvey, Jan 15 '17 at 18:33

score 4 · Answer 1 · edited Jul 03 '17 at 16:48

Take a look to:

Text-based CAPTCHA Strengths and Weaknesses. ACM Computer and Communication security 2011 (CSS’2011). link

The authors present a CAPTCHA breaker and explain a generic algorithm to crack standard CAPTCHAs

In this section we present our captcha breaker, Decaptcha, which is able to break many popular captchas including eBay, Wikipedia and Digg [...] Decaptcha implements a reﬁned version of the three stage approach in 15,000 lines of code in C# [...]

score 3 · Answer 2 · edited May 23 '17 at 12:17

3

This is easier said than done.

This involves either brute-forcing the captcha or running OCR algorithms on it to try and detect what is written in the captcha.

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

It also depends on what techniques were used to produce the CAPTCHA. Some distort the text and some squeeze the text.

Your question is a little vague.

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

Christian

edited May 23 '17 at 12:17

Community

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answered Dec 02 '10 at 02:31

Christian Joudrey

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I'm looking for an OCR engine – Xaqron Dec 02 '10 at 02:32
As SimpleCoder explained, you won't find one to decode all CAPTCHA's. As each CAPTCHA has it's own technique. Do you have a CAPTCHA in particular you are trying to break? – Christian Joudrey Dec 02 '10 at 02:34

score 0 · Accepted Answer · answered Dec 02 '10 at 02:30

There are so many types of Captchas out there that you won't find a single library to read them all. If you are only interested in one type though, you might have more luck. Even then, there are lots of variations on Captchas, and the engines frequently produce (whether on purpose or incidentally) tricky ones which even humans can't figure out. Humans can click the little icon to get a new one; your program might not be able to.

Is there any DECAPTCHA library in .NET?

3 Answers3