I write a script to genreate rand string and image it with imagejpeg, the picture(0.jpg-9.jpg)'s color is red and the picture(a.jpg-f.jpg)'s color is blue, but when I test it I found sometime the color of new image will make some mistake, such as red digital picture became white-blue and the blue digital picture became white-red.

Setting: Apache2.0.44+PHP4.3.1
you can see the demo at http://www.blists.com/image.html
please refresh it some times.
thank you!



<?php
session_start();
$DIR_SET['vcode'] = "http://www.blists.com/images/vcode";
function Vcode($num = "",$type = "") {
 $string = array(
  'digit'=>'0123456789',
  'alpha'=>'ABCDEFGHIJKLMNOPQRSTUVWXYZ',
  'mixed'=>'0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ',
  'shortmixed'=>'01234567ABCDEF'
 );
 $str   = "";
 
 if ($num == "")  $num = 4;
 if ($type == "") $type = "mixed"; 
 
 for ($i=0;$i<$num;$i++) {  
   $offset = rand(0,strlen($string[$type])-1);
   $str .= @substr($string[$type],$offset,1);
  }
 return $str;
}




$str = Vcode(5,"shortmixed");
$_SESSION['vcode'] = md5($str);
header("Content-Type:image/jpeg");

$src_im = imagecreate(100,18);
$x = 0;
for ($i=0;$i<strlen($str);$i++) {
 $image = substr($str,$i,1);
 $dst_im = imagecreatefromjpeg($DIR_SET['vcode']."/".$image.".jpg");
 imagecopymerge($src_im,$dst_im,$x,0,0,0,20,18,100);
 $x+=20;
}
imagejpeg($src_im);

?>