It's the seal around the crankshaft where it attaches to the.... we'll just say where it attaches to the transmission, easier for you to understand probably. The seal is cheap. The labor to do it will destroy your back, arms, clad bone, or bank account. Or all if you're not careful.
But serious, just take it to a shop for professional diagnosis. I'm not mentally Challenged, but I'm not a professionally trained technician either. Pictures aren't always the best for diagnosis. With any luck its something more simple.