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July 17, 2006
Check your user is human. Have him retype a word in a graphic
Do you have trouble with automated programs completing forms on your websites and making cart loads of submissions? Or even just a few spammers submitting their betting ads, performance enhancing pill sites, and share purchase suggestions? And yet you don't want to have to have anyone who wants to use your site register.
Using what has become known as captcha technology, you can display a graphic with some text on what's basically a login page, then have your human user type that text back in. It's very difficult indeed for automata to recongnise the text, and can be doubly so if you vary the background, change fonts between characters and change text colour, scale, rotation. Mind you, you can make it pretty tough for the human too.
You'll find captcha in use already on many big sites, and there are other sites that will host the service for you. Actually, if you've got PHP available and the GD module it's very easy to code it up from first principles and that gives you the ultimate of flexibility.
* Try my demo here
* Show source code of main demo
* Show source code of graphic generator
Posted by gje at July 17, 2006 09:28 AM