I think a good idea would be to make the fields with the images not editable, but then add the custom fields as text in the post. But the custom fields as text, add a function to make it “admin only” or logged-in users only.
That way, only the logged-in person who controls the post and/or admin can change the custom field. Once the author changes the custom field text, the custom field will change with the images too. It can just be placed somewhere on the page where it can all be editable.
