<?php
$file = 'image.png';
$format = end(explode(".",$file));
$key = "abcdefghijklmnopqrstuvwxyz1234567890";
$a = str_shuffle($key);
$name = substr($a,0,6);
$filename = "$name.$format";
if (is_file($filename))
{
$b = str_shuffle(str_rev($key));
$c = substr($b,0,6);
$newfile = "$c.$format";
}...