Function code for randomly displaying pictures in php

For example, the blog display window
Copy the code The code is as follows:
/********************************************** 
* 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/';
}
//The location where image files are stored
$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]");
?>