It's much easier to figure out where it is leaking if you can clean the engine off with engine cleaner first, rinse it off and let it dry. Then see where oil/moisture starts to appear. It always drips down, so the highest area that has oil on it is where you start looking. You may have more than one leak, and from the amount of grime, it looks like it's been leaking for a long time. You never know, it could be coming from someplace easy to access like the valve cover gasket.