Visual Confirmation

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damnian
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Re: Visual Confirmation

Post by damnian »

I've been directed to this topic by an anonymous comment on my site. The author claims to be a member of the phpBB development team. I've got his/her email address, but I don't know who this person is.

I replied asking about the current CAPTCHA development status. I hope it's OK to continue the discussion here.
It is an active project, but it's developement is closed currently (mainly due to the fact that in the CVS is code to crack some of the earlier CAPTCHA's we made and a few public CAPTCHA's (like freecap, which is easy as pie)
I don't think FreeCAP is that easy. Has anybody managed to break it already?
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damnian
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Breaking the phpBB CAPTCHA

Post by damnian »

I have updated the article in question to contain more detailed description. I believe it's still too vague for somebody to implement.

Have a look!
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Re: Visual Confirmation

Post by NeoThermic »

damnian wrote: I don't think FreeCAP is that easy. Has anybody managed to break it already?
Well, based on a similar implementation problem, freecap can be broken.

You can request the same code to be done in a diffrent way by extracting the freecap image URL, and then re-calling the image.

Take, for example, this freecap example image (that I plucked off a site):
Image

We can now try extract just the letters. This is a trivial task, since any background can be seperated rather easally with one pass:
Image

Using a second pass, you can clean the image up enough to get rid of stray pixels:
Image

Next, you can manipulate the image to find points that match the letter. The smaller the red, the less confident the process is that the point it is creating is one that should be used (and can be ignored by the next step);
Image

After that, the points are created in a new image, and linked. Here you can see that a small red dot was ignored because it wasn't confident enough to use it:
Image

Finally, the red dots are removed, and the process turns to attempting to identify the letters. Any letters that it is unsure of will be double tagged (i.e. {first guess}|{second guess}[|{...}]). Only letters which are 85% matched or higher are considered sucessfull and printed:
Image

Trivial ;)

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SHS`
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Re: Visual Confirmation

Post by SHS` »

NeoThermic wrote: Trivial ;)
Go you girl! ;) & :P
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Cheater512
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Re: Visual Confirmation

Post by Cheater512 »

I never got the hang of how the points are generated.
Could you pm me the technique used?
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Re: Visual Confirmation

Post by NeoThermic »

Cheater512 wrote: I never got the hang of how the points are generated.
Could you pm me the technique used?

Serge Belongie, Jitendra Malik and Jan Puzicha did a paper on such techniques in July 2001 which was presented at the Eighth IEEE International Conference on Computer Vision. You might be able to find this paper; it details the techniques behind implementation of such point generation. Do note that the maths are a bit on the wild side, so you'll have to understand them to make good use of the paper.

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damnian
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Re: Visual Confirmation

Post by damnian »

NeoThermic wrote: You can request the same code to be done in a diffrent way by extracting the freecap image URL, and then re-calling the image.
Sure, this needs to be changed.
NeoThermic wrote: Trivial ;)
Indeed, any 1st grader can do this. :lol:

Even if it is breakable, it's a lot harder than what phpBB currently has.
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{o}
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Re: Visual Confirmation

Post by {o} »

Lets animate!
Image
:mrgreen:
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Re: Visual Confirmation

Post by itunes66 »

caych

piece of cake
2 things i like about you hmm.. ill have to get back to you on that one
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{o}
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Re: Visual Confirmation

Post by {o} »

WRONG :twisted:
What caych means?

catch...
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