All pit vipers, including copperheads, have distinctly triangular heads, which is the first give-away as to what one should be contemplating: Fight or flight.
For my money, the first thing should be whether it is running from you. If it is running from you, leave it be. I grew up in Florida where you could stumble across the occasional cottonmouth. We left them alone and they left us alone. Most of nature is like that, and I like it that way.
No need to ask for trouble.
Apparently, TN snakes have a warped sense of humor because some on the non-venomous ones flatten their little heads out to look triangular. The only way I can tell is to eyeball them closely. Discretion being the better part of valor....