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.

Interesting. I saw the MIT license and was wondering (mostly in general, not about this particular case) how that would work. I understand to re-license something, one must hold copyright ownership, and unfortunately, I could imagine imagining companies or even hospitals getting a bit strange about that.

hmmm, good point. i think the copyright issue would be fairly complicated here ... and you'd need a good lawyer basically. it'd likely hinge on how you constructed the argument.