PHP Rename Files in Folder

rename.php

<?php
$dir = 'images/';
$files = scandir($dir);

foreach($files as $i => $name) {
    if($i > 2){
        $filename = $name;
        $newname = $i-2 . '_' . $filename;
        if ($newname != $filename) {
            rename($dir.$filename, $dir.$newname);
        }
    }
}