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: 
zuojiankuohaophpcn?php 
/********************************************** 
* filename : img.php 
* author : freemouse 
* web : www.cnphp.info 
* email :freemouse1981@gmail.com 
* date : 2016/10/30
* 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]"); 
?>