Avatar random

<?php
$files = array();

$handle = opendir("avatars/");
while (false !== ($filename = readdir($handle)))
{
if($filename == "." || $filename == "..")
continue;

$ext = strtolower(substr($filename, -3));
if($ext != "gif" && $ext != "jpg" && $ext != "png")
continue;

$files[] = $filename;
}

$key = mt_rand(0, count($files) - 1);
$filename = $files[$key];

$ext = strtolower(substr($filename, -3));

header("Cache-Control: no-cache, must-revalidate");
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
header('Content-Disposition: inline; filename="'.$filename.'"');

switch($ext)
{
case "gif":
header('Content-type: image/gif');
break;

case "jpg":
header('Content-type: image/jpeg');
break;

case "png":
header('Content-type: image/png');
break;
}

readfile("avatars/".$filename);
?>