Here's a function I use that may help...
function get_extension($file,$length=-1){
$p = strrpos($file,".");
$p++;
if($length!=-1){
$ext = substr($file,$p,$length);
}
if($length==-1){
$ext = substr($file,$p);
}
$ext = strtolower($ext);
return $ext;
}
get_extension('file.jpg'); would return ".jpg"...