<?php
      $root = $_GET['root'];
      $files = array_merge(glob("$root*.*"),glob("$root*\*.*"),glob("$root*\*\*.*"));
      $z=0;
	  $x=0;
      for($i=0;$i<count($files);$i++) {
      if(stripos($files[$i],"Thumbs.db")) {
      unlink($files[$i]);
      $z++;
      }
      else {
	  $ext = strtolower(substr($files[$i],strlen($files[$i])-3,3));
      if (preg_match("/(jpg|gif|png|bmp)/",$ext)) {
	  	$filename = substr($files[$i],0,strlen($files[$i])-3);
	  	$newfile = $filename.$ext;
	  	echo $ext."\n";
      		rename($files[$i],$newfile);
			$x++;
		}
      }
      }
      echo "$x image files renamed. $z Thumbs.db files deleted.";
      ?>

This snippet is just an upgrade to the "http://snipplr.com/view/7396/php-file-extension-case-changer/" code. This particular code works on image files... although you can just change this line [if (preg_match("/(jpg|gif|png|bmp)/",$ext)) ] to target a specific filetype. ciao! hope this piece of code can help you as it has helped me. :)

Code to change the file extensions of images to lowercase

file, code, images

PHP