Here are the steps:
1. select post to edit
2. select image field and select image
3. once selected, on the change event (from your example – thanks!) update a text field with the id of the image
4. then get this id value via PHP (my code that doesn’t work) so that I can access the URL of the newly selected image.
You are right I can probably do it all with javascript, just felt like it would be cleaner this way.
I am no PHP expert so not sure if I can really call a PHP script multiple times or if PHP is really only called once.