On Sun, 2007-06-10 at 12:27 +0900, Dave M G wrote: > PHP General List, > > With a little help from the web, and help from this list, I have a > simple CAPTCHA image that works within the content system I'm building. > > But it's *really* simple. Basically white text on a black background, > with a couple of white lines to obscure the text a little. > > I'm pretty sure that in its current state, my CAPTCHA image could be > cracked by OCR software from the 1950s. You're probably right :) > So I'm hoping to take it up to the next level. > > I might be able to figure out how to add more lines, more colours, and > those kind of basic changes. > > But what I definitely can't comprehend is how some CAPTCHAs have that > really warped and distorted text. They do x,y shifting, blurring, and various other techniques. > Is that possible with PHP? Do I have to make a library of pre-warped > text images or something? No, PHP can do it. If you can work with pixels (and you can) then you can do any advanced mutation of an image... the only issue is how long it takes to perform the mutations. > Is it possible to make backgrounds that are really crazy with textures > and gradients. Would that also rely on a pre-built library of images? It can rely on a pre-built library of images (I recently integrated freecap into a website that uses this technique (amongst others) for generating the background). It can also be done programmatically (fractals would be a good example). > Can someone maybe point me to an online instructional on how to get a > CAPTCHA image that really works? Check out the freecap code perhaps (my eyes, my eyes, the code is hideous). Check out other CAPTCHA scripts also. Learn from the techniques they've employed, then roll your own if you still want to create your own master CAPTCHA system :) > Tips on what differentiates a good CAPTCHA from a bad one would also be > really sweet. Good CAPTCHA - bots can't figure it out Bad CAPCTHA - bots can figure it out ;) For what it's worth, and my experience with OCR is limited, the main idea is to make it difficult to determine the characters by thwarting edge detection and statistical models of pattern colour distribution. Also keep in mind that you want people to be able to understand it. The freecap system made some really unintelligible CAPTCHAS until I tweaked the settings. Additionally many characters looked like many others when morphed so I pared down the possible characters to less ambiguous possibilities. Cheers, Rob. -- .------------------------------------------------------------. | InterJinn Application Framework - http://www.interjinn.com | :------------------------------------------------------------: | An application and templating framework for PHP. Boasting | | a powerful, scalable system for accessing system services | | such as forms, properties, sessions, and caches. InterJinn | | also provides an extremely flexible architecture for | | creating re-usable components quickly and easily. | `------------------------------------------------------------' -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
