random-avatars.php

<?php
$type = array('jpg', 'jpeg', 'gif', 'png');
$dir = './pic';

if($handle = opendir($dir)) {
  while(false !== ($file = readdir($handle))) {
    $ext = pathinfo($file);
    $ext = $ext['extension'];
    if($file != "." && $file != ".." && in_array($ext, $type)) {
      $files[] = $file;
    }
  }
  closedir($handle);
}

$name = rand(0, count($files) - 1);

if(@$_GET['action'] == '.gif') {
  $randfile = $dir.'/'.trim($files[$name]);
} else {
  $randfile = "noavatar.gif";
}
$file_ct = mime_content_type($randfile);
header("Cache-Control: no-cache, must-revalidate");
header("Content-Type: $file_ct");
readfile($randfile);
?>