php中随机显示图片的函数代码

例如博客的展示窗 
复制代码 代码如下: 
/**********************************************
* Filename : img.php
* Author : freemouse
* web : www.cnphp.info
* email :freemouse1981@gmail.com
* Date : 2016/10/30
* Usage:
*  
*  
***********************************************/ 
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]"); 
?>