NYCPHP Meetup

[Daniel Convissor]

Hi Joel:

Getting back to this aging thread...

On Thu, Jul 22, 2004 at 04:06:02PM +0000, Joel De Gan wrote:
> Are you talking about how to keep crackbots out? or how to crack one one
> of these?

Keeping crackers out.


> I have done a lot of work in cracking captcha's (and have published code
> all over about it).

Thanks for your great advice.

I have a few questions...

* Does it matter what type of image is used?  I'd guess JPEG's lossy,
somewhat imprecise, nature would be a _little_ harder for bots to 
decipher.

* I'm using fuzzy fonts, but they may be a bit _too_ fuzzy for humans 
to easily figure out.  I'm pondering if it would be better to use 
cleaner fonts, but split each letter in half along a random axis and 
then move the two halves apart a little bit in a random direction.  
This would likely thwart attempts to use the font files to reverse 
engineer the characters.


Anyway here's my CAPTCHA implementation thusfar...

The source of the image generation is at:
http://cvs.php.net/co.php/pearweb/public_html/captcha-image.php

and the value generation is at the bottom of:
http://cvs.php.net/co.php/pearweb/include/pear-format-html.php

In order to allow testing before deployment, the code I posted doesn't
generate images on the form pages yet.  To see what the CAPTCHAs look
like, go to this page to initialize a captcha session var:
http://pear.php.net/bugs/bug.php?id=14&edit=3

Then view the image here:
http://pear.php.net/captcha-help.php

Please let me know what you think.


> The main issue here with this one is the random line(s) and the opacity.

Opacity?  How would I tweak that for a particular object?  I didn't 
see any related functions in the php gd man page.  I am juggling 
colors, though.

Thanks,

--Dan

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