Надежная и в то же время простая captcha на php.

                        
<?php

// by Jahak

session_start();

$md5_hash = md5(rand(0,99999)); 

$security_code = substr($md5_hash, 25, 5); 

$enc = md5($security_code);

$_SESSION['captcha'] = $enc;



$width = 150;

$height = 30; 



$image = ImageCreate($width, $height);  

$white = ImageColorAllocate($image, 255, 255, 255);

$black = ImageColorAllocate($image, 0, 0, 0);

$grey = ImageColorAllocate($image, 200, 200, 200);



ImageFill($image, 0, 0, $white); 

ImageString($image, 10, 5, 0, $security_code, $black); 



header("Content-Type: image/png"); 

ImagePng($image);

ImageDestroy($image);



?>