Load Captcha Image to Let User Type it

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Hi There

I have made some code that uses HttpWebReques to let the user login to a website that uses form. (POST Request). Now I have some sites that require to the fill in an captcha image when logging in. Posting the extra field is no the problem but showing the image to the user and ask for the value and use it in the POst request isn't really working now.

I know where the images are located but when I surf to the login page like here:
(Sorry for the p0rn, is the only security system I could think where I have a problem)

[LINK DELETED]

Is the login url, and the captcha image is located here:
/cgi-bin/sblogin/turingimage.cgi?Sunday, 17-Jul-2011 03:42:26 EDT[^]

(Time and data changes) But when I go to the image url I get another image then I had when viewing the login form. I know the turingimage.cgi is suposes to give you an random image when it gets requested.

But How the hell can I login to the website with showing the user of my program the correct captcha ?

I tried using the cookies of the first request but that didn't work.
It would be nice if somebody could help me out.

McPhantom

[edit]Link to pr0n deleted. Please do not post such links again, or you will be reported, and may end up banned. SFW links only, please - OriginalGriff[/edit]

[Edit this was posted as a reply, it is really a comment on my answer - KBarrow ] I think yu get me wrong xD I do not want to add a captcha to my site I want to login to a website who use one.

Posted 16-Jul-11 21:50pm

McPhantom

Updated 17-Jul-11 22:12pm

Keith Barrow

v3

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Keith Barrow 18-Jul-11 4:18am

The whole point of Capcha is to prevent automated logins, by helping you do this we are helping to circumvent the host site's security. Even if the intent is good I doubt you'll get much help here.

McPhantom 19-Jul-11 4:03am

That's true but the the purpose of a captcha is more preveting bruteforce attacks.
I don't see the difference between logging in trough a tool and let the user enter the value of the capthca > get some info and log out?

That's different then trying to read the captcha image using an OCR engine or decaptcha.

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Keith Barrow · Answer 1 · 2011-07-17T02:40:00

Typically you'd use a third party control to generate this stuff, there are freeware ones. The is one available in the CodeProject: "A CAPTCHA Server Control for ASP.NET[^]"

Just returning pre-defined static images is no good, a bot will be able to parse the html and know what it is, so it all needs to be done on the fly and preferable with random "noise" to prevent OCR training.

Nice to see you have such rarefied tastes in pr0n BTW :). A better stratgey would be to take a screen shot cut out the relevant bits and upload to http://imgur.com/[^]. This has two benefits: people answering questions won't get sacked from downloading porn at work, and you won't get banned from the CodeProject ;)