I don't think copyright applies to the image itself. The work of curation can be copyrighted, but here it's trivial, just selecting one image. If he published a book of AI-generated artwork, the curation of images could be copyrighted as a whole, but each individual image would not be copyrighted.
What happens if he doesn't publish the book during his lifetime, and later his estate decides to release it but no matter how hard people try, nobody can figure out whether or not any AI was employed?
