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Block Spam Bots With Free CAPTCHA Service
Chirag Mehta writes "I just released a freeware service called BotBlock (barebones demo) that lets site owners copy/paste a few lines of PHP code and insert a CAPTCHA image-verification system into any web form. The amount of form spamming by bots is on a rise. While remedies exist for MT blogs, a more efficient solution is to use image-verification or text-identification. Used for a while by sites like Yahoo! (scroll to bottom), Hotmail and patented in 2001 by AltaVista, CAPTCHAs are now being used more widely. PARC also came up with two algorithms Baffletext and Pessimal Print. The technology always existed, but until now required the site owners to install image libraries and understand how to generate images that cannot be OCR'ed. With BotBlock it is like inserting a page counter."
much better than blacklists and captcha is a bayesian filter.
blacklists are innaccurate: blacklisted words can be misspelled and pass through.
captcha discriminates against the disabled and cuts them off from online discussions.
James Seng has crafted a good bayesian filter for movable type.
They have one that generates sounds. You're in trouble if you're blind and deaf, though.
Scratched Emulsion
For my GPL'ed PHP Captcha sofware:
http://sourceforge.net/projects/session-captcha/
I'm working on another version, which I believe is unique at this point. (At least I didn't find anything like in on Google a few weeks ago).
See a sample at the link below. (DISCLAIMER:: This site is a small self run hosting company, and has "sales" links, and is of commercial nature. So if you're going to get all pissed off because I am trying to feed my kids please do not click through. The sample does not collect or log anything outside of what Apache routinely collects. ) http://webshowhost.com/main.php?smPID=PHP::ui_huma n_verify.php&caseFlag=SAMPLE
What makes this implementation unique is that in the pattern user must identify color and characters. It combines multiple levels of recognition. The user must understand the concept of COLOR and the characters. This should make it particularly difficult for SPAM bots to dicipher, since color is very subjective. I am posting this here mainly to establish prior art (as I have not seen any test use these concepts before) in case some joker tries to patent this variety of CAPTCHA.
My variety integrates into a toolkit I've developed, but basically uses imagemagik montage to fuse pre-rendered image bitmaps into a single JPEG.
It is obviously weak in the sense that it discriminates against blind folks and illiterate folks. On the bright side it has definately eliminated ALL of my spam!
If your interested in this contact me at captcha1@webshowpro.com ** Note you'll have to verify yourself with the prototype system to sendmail to that account.
I'll do my best to provide you with the relevent code. I don't have time at this point to lead a project (as my company is a oneman show barely scraping by at this point). So my apologies in advance if I cannot support the code to your satisfaction.