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Improvement

Andrew Hull has improved on my captcha-code; he obfuscated the text even more than I have. He wrote:

Have a look through the code before you post it, I have made a few changes since yesterday, it can randomize the font and you might like to add random swirly function (pick one of sin x^2, 1/2sin(x) that sort of thing). You could also add a slope to the function (y=1/2x), or use a parabolic. Have a play with the variables, and you will see things become very wooly without being too unreadable.

Obviously you have to watch out for the text becoming completely unreadable. BTW wikipedea has a good section on captcha, detailing how bots try to get round it. I was looking to make PHPbbs more secure, and since it seems their inbuilt captcha can be fooled, I thought I'd look for a replacement, and that's how I stumbled on your code.

The idea of using noizified colours is really to fool the bots, since they generally look for a particular colour in the flattened image for their pattern recognition. Noizifying the font edges again is designed to break their OCR, and randomizing the font makes life even more complex for them.

The source of his variant is downloadable here. An example of how it looks:

(This is the default setting; the captcha can be made more/less readable by adjusting parameters.)

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14 comments

Borg wrote at 2 Feb 2017, 11.48:

Captcha is the most annoying thing on the internet since it appeared. It's stupidity starts with images so barely visible that less than 1% of people can actually see what's there and ends up with giving you 5 turns of half-right options to click on. If something totally sucks on the internet it's the captcha.

joe wrote at 18 Feb 2015, 16.19:

this is cool.

generic viagra wrote at 31 Oct 2010, 15.24:

buy viagra canadian pharmacy lulz!!!!

David_quick wrote at 27 Aug 2010, 19.16:

The problem with this type of thing, while effective is that it is also very effective at excluding colorblind people. For instance, i had to have someone read off the captcha here so that I could post this.

nmr wrote at 31 Dec 2009, 11.32:

great work

wow power leveling wrote at 14 Apr 2009, 10.07:

This is great! Now I want to see your ways for us readers to become more involved! Expect an email later today

Chris wrote at 16 Jun 2007, 1.51:

Nice piece of work. For the forum I'm administrating these days, I've moved away from captcha. I've simply added questions instead using some PHPbb mod. I can only speculate it working better when the questions and answers aren't in English (as they would be machine readable with no translation needed). It's stupidly simple and it works amazingly well. Using questions like (although not in English): Type nisse into the box to the right: [box] Type hello into the box to the right: [box] We've not had -1- spambot get trough it since it was set up 2-3 months ago. Quite amazing.

Comrade Smack wrote at 14 May 2007, 20.32:

Personally, My favorite captcha is the "Which of these pictures has an owl" where you could pick a number or click it. With the exception of Captcha sweatshops I don't know how there could be an easy way around those. Of course, blending the two you could have distorted text at the bottom of a set of four animal pictures, then be told something like "enter the text under the monkey eating a fish" or something similar. This involves more overhead but would still be similar for a human and devilishly difficult for a computer.

Kisom wrote at 19 Mar 2007, 18.10:

Great work. I run a modified version of this code on my website @ http://dreamsters.se/reg.php.

AJH wrote at 2 Jan 2007, 14.07:

Ooops, I see this doesn't preserve the line breaks. Bother! If you want the modified version, try AhUll AT theclydegroup dort com

Steevg pAQUE wrote at 28 Dec 2006, 16.25:

SALUT C COOL

Aziz wrote at 13 Oct 2006, 14.45:

I just wanted

Pramod Ghuge wrote at 3 Oct 2006, 20.12:

you have done a great job with this topic

Sprite_tm wrote at 29 Sep 2006, 17.58:

Oopsie, someone commented on the captcha-code being readable from the img-tag here, but I accidentally lost the comment. Suffice to say: the problem has been addressed on my site, the solution for other sites remains an excersize for the reader :)

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