To identify a snake from a sloughed skin usually requires a count of mid body scale rows and a look at the arrangement of the head shields (scales on top and side of head). This can be very hard to do from a photograph but is easy to do if the skin is carefully collected (to include head and a large section of the middle body area).
I should add that the the underside of the entire tail section should also be photographed or collected (in order to count the number of divided and entire underside (subcaudal) scales)