Captchas are images frequently used on web pages to preven the access of automated robots to web pages. The generally consist of an image of text, distorted such that a computer cannot read it, but a human can. The user is then required to type the text in the image into a box, and the web server checks to see if the letters were typed correctly. This is an ideal implementation; however, programmers are constantly trying to beat automated reading robots while trying to have the images remain readable by actual humans.
Captchar is a simple captcha written in PHP. It requires the GD library and PHP 5 to run. Here's how it looks like:
Strengths of this implementation include the light weight and ability to use a pre-defined wordlist (which you see above). It is also relatively difficult for computers to read compared to similar implementations found on the internet, though not as strong as those used professionally.
Admittedly, since it was meant for personal use, it is also difficult to customise. However, the code is relatively small (150 lines), so it should be easy enough to figure out.
Some other features include error handling, only easy-to-read letters and words and random color generation.
Download
You can download the source (txt, 5KB) and put it on your webserver and try it out yourself. You may also want the default worldlist (txt, 39KB) and the following font files: font.ttf (268KB) and fonta.ttf (59KB).
Using it is really simple. After you've included captcha.php into your php file, just use the following:
To generate an image:
$captcha = new Captchar();
$captcha->generateImage(320, 75, 10);
To validate user input:
if($_SESSION['captcha'] == $user_input && $_SESSION['captcha'])
return true;
else
return false;