Since Joel-Peter Witkin says he uses unclaimed bodies from a Mexican morgue, I will not coment on the aesthetics of his work due to issues of consent of his subjects. It is interesting to note if he tried to do this in America, he would be jailed, the morgue would pay millions in restitution, and the pictures would be ordered destroyed.
I say this based on the recent outcome of the Thomas Condon case, another "morgue artist", the details of which can be found here:
Unclaimed bodies from a Mexican morgue also deserve respect and protection. Even if we don't know it, "Glass Man" once had a name of his own.