I'm not sure how definitive that guide is. For what it's worth, all of my medical textbooks are very careful to include licensing and attribution information fo

I'm not sure how definitive that guide is. For what it's worth, all of my medical textbooks are very careful to include licensing and attribution information for all of their medical images, including X-rays. So even if there's not much case law on it, publishers seem to be erring on the side of caution.