I'm running a theme that has a custom post types built in, and essentially what I need to do is display a book cover on the post (actually a custom post) page when the ISBN was already entered into a custom field when the post was created.
I understand the link that shows info from Google Books, but what I do not understand is how to pass that info onto WordPress (or even where to begin!). I would very much appreciate it if someone could at least point me in the right direction.