my next work is a very simple image captcha php class which simple prints a random image with string on it which is very useful for security purposes.
the file could be downloaded from http://nasaralla.googlecode.com/files/captcha.php
and the simple to use instructions are as follows:
//include the class file
//instanciate the class
$c = new Captcha();
//generate the random string with this function
//print the image