For the majority of people, a leopard is a leopard. Sure there are quite a range of subspecies, but one generally looks rather like the other. Indeed the only significant difference people often notice is one that has not justification – that of the melanistic leopard (or black panther)
In order to disturb wild leopards as little as possible, the study took DNA samples from museum held leopard specimens all over the world.
African Leopard 
Asian Leopard