Thumbnail snippet problem

I just tried to make a snippet create an on-the-fly thumbnail so I basically modified this file:

http://wv4.co.uk/code/create-php-thumbnails-on-the-fly.txt

But it doesn’t seem to let me set the headers for the output and instead outputs the image as characters. Is this not possible? Is there another way, like make an ajax call to an external script?

Ok my current workaround is to create a php file and have the img tag point to that eg. <img src="assets/thumbnail.php?im=[[+tv.img]]" /> and then in the script prepend the base path to the ’im’ variable.