This is the Nazgul king, the Witch-king of Angmar, leading his force from Minas Morgul towards Gondor.
Well, not really. It's probably just some Black knight from Heroes of Might and Magic.
But since Heroes of Might and Magic has been heavily inspired by Lord of the Rings, it's not surprising that this artwork could resemble a scene in the book. I mean, look at it: A black horseman leading an army of orcs, dark wizards and corrupted humans from a dark, shadowed city. This artwork is fu**ing awesome.