I've discovered a workaround for using an image in place of the story title, but it's not ideal. For now, I've simply hosted the image then inserted the standard 'img src=...' tag into the title field.
This works, but means I have a long img src tag as the title, which looks odd on the save file and in the editor itself.
I discovered the CSS for the title is #story-title
, but when I inserted the image url into the CSS it resulted in both my image AND the default title showing.