An image field holds the attachment (post) id of an image, so this is why the images do not appear. ACF doesn’t know what to do with the text that it’s finding so it ignores it.
You might be able to do something with this http://www.advancedcustomfields.com/resources/acfload_value/, but I’m not sure how. In your filter you’d need to take the url and somehow convert it to an image ID. You could try searching for something like: Get an attachment ID by URL in WordPress
