一个PHP验证码类代码分享(已封装成类)

<?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));
}
public function createimg()
{
$_session['check_pic'] = $this->codes;
$img = imagecreate(70,25);
imagecolorallocate($img,222,222,222);
$testcolor1 = imagecolorallocate($img,255,0,0);
$testcolor2 = imagecolorallocate($img,51,51,51);
$testcolor3 = imagecolorallocate($img,0,0,255);
$testcolor4 = imagecolorallocate($img,255,0,255);
for ($i = 0; $i < 4; $i++)
{
imagestring($img,rand(5,6),8 + $i * 15,rand(2,8),$this->codes[$i],rand(1,4));
}
imagegif($img);
}
}
$code = new securitycode();
$code->createimg();
$code = null;
?>