PHP簡單驗證碼

<?php
session_start();
Header("Content-type: image/gif");
class SecurityCode
{
private$codes='';
function __construct()
{
$code='0-1-2-3-4-5-6-7-8-9-A-B-C-D-E-F-G-H-I-J-K-L-M-N-O-P-Q-R-S-T-U-V-W-X-Y-Z';
$codeArray=explode('-',$code);
shuffle($codeArray);
$this->codes =implode('',array_slice($codeArray,0,4));
}
publicfunction CreateImg()
{
$_SESSION['codes'] =$this->codes;
$img= imagecreate(70,25);
imagecolorallocate($img,222,222,222);
$testcolor1= imagecolorallocate($img,255,0,0);
$testcolor2= imagecolorallocate($img,255,255,255);
$testcolor3= imagecolorallocate($img,0,0,255);
$testcolor4= imagecolorallocate($img,255,0,255);
for ($i=0; $i<4; $i++)
{
imagestring($img,rand(2,5),8+$i*15,rand(2,8),$this->codes[$i],rand(1,4));
}
imagegif($img);
}
}
$code=new SecurityCode();
$code->CreateImg();
?>