Hi All i was having a few problems outputting png's with this script.
Would just output the URL, i fixed the problem but thought i would share the answer if anyone else faces the same issues
PHP 5.1's imagepng function take 3 paramaters, the final paramater is the quality whihc must be between 0 and 9 inclusive.
The default for this script is 100 , change it so somethign below 10 and your png's will work.
Hope this helps someone.
By the way Zubrag, very nice script, modular, easy to use, effective. Keep churning out that code