Ganti header secara otomatis

Script di bawah ini berfungsi mengganti header secara otomatis setiap kali web berganti halaman, buat satu folder berisi beberapa file header yg berukuran sama.. dgn format .jpg

<?php

/**
 * randomly select an image from the current directory and return it
 *
 * @todo - consider accepting a local path as $_GET['img'] for overrides
 * to remain compatible with Marinelli's rotate.php
 *
 * (but why? why possible use case is there for linking to
 * rotate.php?img=file.gif instead of straight to file.gif?)
 */

$file_types = array(
  'gif'  => 'image/gif',
  'jpg'  => 'image/jpeg',
  'jpeg' => 'image/jpeg',
  'png'  => 'image/png'
) ;

$regex = '/\.(' . implode('|',array_keys($file_types)) . ')$/i' ;
$files = array() ;

$directory = opendir(".");
while ( FALSE !== ($file = readdir( $directory )) ) {
  if ( preg_match( $regex, $file ) ) {
    $files[] = $file ;
  }
}

if ( !empty( $files ) ) {

  $which   = rand(0,sizeof($files)-1) ;

  if ( $file = file_get_contents( $files[$which] ) ) {

    $parts   = explode('.',$files[$which]) ;
    $ext     = strtolower($parts[sizeof($parts)-1]) ;
   
    header( "Content-type: " . $file_types[$ext] ) ;
    header( "Expires: Wed, 29 Jan 1975 04:15:00 GMT" );
    header( "Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT" );
    header( "Cache-Control: no-cache, must-revalidate" );
    header( "Pragma: no-cache" );

    print $file ;
 
  }

}