Check CAPTCHA image for readability

goes along with site checks i guess

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6 Replies - 3688 Views - Last Post: 13 May 2008 - 07:42 AM

#1 rgfirefly24   User is online

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Check CAPTCHA image for readability

Posted 01 May 2008 - 10:09 AM

So i have this CAPTCHA image that i've created:

Attached Image

what do you think of its readability?
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#2 Martyr2   User is offline

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Re: Check CAPTCHA image for readability

Posted 01 May 2008 - 11:48 AM

I find it pretty reasonable if the number is 82372. I am not sure how strong it would be against the bots since the only white on the image is pretty much the number (and yeah the line but still). You may want to add some kind of warping effect on the numbers which is harder to calculate. Think what would happen if they took the image and threw away color information and made it greyscale. The number sticks out like a sore thumb.

Just a few things to consider. :)
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#3 rgfirefly24   User is online

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Re: Check CAPTCHA image for readability

Posted 01 May 2008 - 09:07 PM

View PostMartyr2, on 1 May, 2008 - 11:48 AM, said:

I find it pretty reasonable if the number is 82372. I am not sure how strong it would be against the bots since the only white on the image is pretty much the number (and yeah the line but still). You may want to add some kind of warping effect on the numbers which is harder to calculate. Think what would happen if they took the image and threw away color information and made it greyscale. The number sticks out like a sore thumb.

Just a few things to consider. :)



here is the thing. an OCR reader does several things.

1. Removes backgrounds and small lines

2. Segments out the image based on where it reads a letter stops(why i put the gold OCR in the backgroup)

3. Grabs the interpreted letters from the segmented parts. So even if you warp the numbers an OCR reader can still read them. What has to happen is there needs to be some overlap where the OCR reader cant distinguish where one letter stops and the other begins. Thus rendering it incapable of segmenting the image.
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#4 RodgerB   User is offline

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Re: Check CAPTCHA image for readability

Posted 02 May 2008 - 07:01 AM

Another fact: Most OCR's are really crap and often mistake I's for 1's. ;)

Warping characters so they overlap = OCR fail. It's just OCR technology is open-source now, like tesseract, gocr etc, so a smarty might one day decide to attack your website by modifying the OCR engine to do his or her bidding, hence robust CAPTCHA's = way to go.
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#5 rgfirefly24   User is online

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Re: Check CAPTCHA image for readability

Posted 02 May 2008 - 01:15 PM

View PostRodgerB, on 2 May, 2008 - 07:01 AM, said:

Another fact: Most OCR's are really crap and often mistake I's for 1's. ;)

Warping characters so they overlap = OCR fail. It's just OCR technology is open-source now, like tesseract, gocr etc, so a smarty might one day decide to attack your website by modifying the OCR engine to do his or her bidding, hence robust CAPTCHA's = way to go.



The only real safe thing to do is use 3D-CAPTCHA, but since the client doesn't want to use that i am stuck with creating my own. Saying that if a smarty wants to attack my website then no amount of CAPTCHA i have will ever protect me 100%. The only way to mostly stop it is using NoBot which is included with AJAX ToolKit.
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#6 srtech   User is offline

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Re: Check CAPTCHA image for readability

Posted 06 May 2008 - 06:30 PM

Hmm... I can read it, but anyone with slight vision problems may have trouble. Can you post a few more samples so we can see how it changes?
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#7 rgfirefly24   User is online

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Re: Check CAPTCHA image for readability

Posted 13 May 2008 - 07:42 AM

View Postsrtech, on 6 May, 2008 - 06:30 PM, said:

Hmm... I can read it, but anyone with slight vision problems may have trouble. Can you post a few more samples so we can see how it changes?



i have actually totally revamped it from the one you see here. It now uses rotating common backgrounds and asks the user to tell me what the color of the background is. Since OCR readers remove background color then they will have almost a 0% chance of breaking it.
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