regarding note from rehfeld dot us :
In my experience the best( and easiest ) way to find the extension of a file is :
<?php
// use this when you are sure it actually has an extension.
$extension = end(explode(".", $file_name));
?>
or
<?php
// this one will also check if it actually has an extension
$parts = explode(".", $file_name);
if (is_array($parts) && count($parts) > 1)
$extension = end($parts);
?>