php中随机显示图片的函数代码

<?php
/**********************************************
* Filename : img.php
* Author : freemouse
* web : www.cnphp.info
* email :freemouse1981@gmail.com
* Date : 2010/12/27
* Usage:
* <img src=img.php>
* <img src=img.php?folder=images2/>
***********************************************/
if($_GET[folder]){
$folder=$_GET[folder];
}else{
$folder=/images/;
}
//存放图片文件的位置
$path = $_SERVER[DOCUMENT_ROOT]."/".$folder;
$files=array();
if ($handle=opendir("$path")) {
while(false !== ($file = readdir($handle))) {
if ($file != "." && $file != "..") {
if(substr($file,-3)==gif || substr($file,-3)==jpg) $files[count($files)] = $file;
}
}
}
closedir($handle);

$random=rand(0,count($files)-1);
if(substr($files[$random],-3)==gif) header("Content-type: image/gif");
elseif(substr($files[$random],-3)==jpg) header("Content-type: image/jpeg");
readfile("$path/$files[$random]");
?>