another sig php question from sabe

[sabret00the]

this script is meant to give me a random image script usable on forums such as this

PHP Code:

<?php
// usage: [img]http://www.ebslive.com/sig.png/[/img]
// read folder
 $folder=opendir(".");
 while ($file = readdir($folder))
 $names[count($names)] = $file;
 closedir($folder);
// sort file names in array
 sort($names);
// remove any non-images from array
 $tempvar=0;
 for ($i=0;$names[$i];$i++){
  $ext=strtolower(substr($names[$i],-4));
  if ($ext==".jpg"||$ext==".gif"||$ext==".jpeg"||$ext==".png"){$names1[$tempvar]=$names[$i];$tempvar++;}
 }
// random
 srand ((double) microtime() * 10000000);
 $rand_keys = array_rand ($names1, 2);
// random image from array
 $woot=$names1[$rand_keys[0]];
  header("Cache-control: max-age=31536000");
  header("Expires: " . gmdate("D, d M Y H:i:s",time()+31536000) . "GMT");
  header("Last-Modified: " . gmdate("D, d M Y H:i:s",time()) . "GMT");
  header("Content-disposition: inline; filename=sig.jpg");
  header('Content-type: image/jpeg');
  $im = imagecreatefromjpeg("$woot");
  imagealphablending($im, true);
  imagejpeg($im, "", 80);
?>

however it's not quite working like that, in alot of cases, i prefer to use png's either due to the size, loading speed or superior ability when it comes to transparency, but when i try and use this script i seem to get this error quite a bit

<br />
<b>Warning</b>: imagecreatefromjpeg(): gd-jpeg: JPEG library reports unrecoverable error: in <b>/home/ebslive/public_html/sig.png/index.php</b> on line <b>34</b><br />
<br />
<b>Warning</b>: imagecreatefromjpeg(): 'ebs-banner.png' is not a valid JPEG file in <b>/home/ebslive/public_html/sig.png/index.php</b> on line <b>34</b><br />
<br />
<b>Warning</b>: imagealphablending(): supplied argument is not a valid Image resource in <b>/home/ebslive/public_html/sig.png/index.php</b> on line <b>35</b><br />
<br />
<b>Warning</b>: imagejpeg(): supplied argument is not a valid Image resource in <b>/home/ebslive/public_html/sig.png/index.php</b> on line <b>36</b><br />

this or something very quite similar, how can i fix this?