According to Gloyd and Conant, the major characters are white edging along the darker crossbands (this one has), wider crossbanding at midbody (this one has pretty narrow bands), and a single row of scales separating the crossbands from the ventrals (you can see this in the second photo).
I'm unconvinced that there really is a subspecific difference between northerns, southerns, and osage, but the coloration of this snake was breathtaking. I've never seen such an orange/rusty copperhead before. Interestingly, I also saw a second copperhead at the same site today that looked virtually identical, but about 3/4 the size. Unfortunately, it got away into tall and thick grass before I could get a pic. Shoulda brought the tongs lol
Van