1) we need an absolute path for the image, since it needs to be retrieved

1) we need an absolute path for the image, since it needs to be retrieved
by the external editor helper application (NB: that fatal error was probably
a PHP 4/5 thing, I'm using PHP 5 here).

2) adding some extra information for the helper, this should all be made
a little more logical (only pass on as much information as needed to
construct the proper URLs)