<?php
session_start();  
$alp='QWERTYUIPASDFGHJKLZXCVBNM123446789';  
$len=strlen($alp);  
$code=NULL;  
$image = imagecreatetruecolor(72, 30);  
$x = NULL;  
$chars = mt_rand(4, 6);
for($i=0; $i<$chars; $i++)
    {
    $x+=rand(7, 11);  
    $code .= $symb = $alp{mt_rand(0,$len-1)};  
    imagechar($image, 5, $x, mt_rand(2, 14),$symb, 0x00FFFF);
    }  
$_SESSION['code'] = strtolower($code);  
imagefilter($image, IMG_FILTER_EMBOSS);  
header('Content-Type: image/png');  
Imagepng($image);  
ImageDestroy($image);
?>