On Sat, June 9, 2007 10:27 pm, Dave M G wrote: > 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. But does anybody CARE enough about whatever you have to spend the time to write an OCR routine to defeat it? I suspect the answer is "No" In which case you are just wasting your time making it "tougher," not to mention making it harder on real humans to actually use the dang thing. I put a CAPTCHA on a site with zero (0) distortion, noise, or anything remotely resembling anti-OCR, and haven't had a junk post in years. Had thousands a day before that, so it works. > 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. You can define a "transformation" in various axes, or with random matrix manipulation of an image. There are all kinds of image-mapping/transforming/projecting algorithms of that nature. It's the same way Photoshop "warps" an image onto a coffemug or whatever shape you want. > Is that possible with PHP? Do I have to make a library of pre-warped > text images or something? Nah. You have to have a library or random-generation of transforms, and a simple routine to apply them. > 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? Sure, you can. And then humans can't read the dang things either. :-) > Can someone maybe point me to an online instructional on how to get a > CAPTCHA image that really works? They all work. :-) Seriously. Wait until somebody hates you enough to spend 40 hours feeding your images to OCR to crack it. I suspect you'll never have a problem. > Tips on what differentiates a good CAPTCHA from a bad one would also > be > really sweet. No comment. :-) -- Some people have a "gift" link here. Know what I want? I want you to buy a CD from some indie artist. http://cdbaby.com/browse/from/lynch Yeah, I get a buck. So? -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
