Off the top of my head (and back of my hand)...
Insulin users and (a-hem) junkies might have some trouble with this.
The US already outlaws back of the hand tatoos as being 'dangerous'...since the vein system which serves as medicines best IV entry point is so
easily damaged. Plus tats make it easy to hide needle entry points.
This seems like a stretch for an ID system, though I could see it being used to find changes in vein structure. You know, busting junkies.