The problem with distinguishing between the rear main, oil pan seal, or other leaks from the back of the engine, is that the oil pan makes a lip that juts out pas the rear of the block. Anything leaking there, whether it be the rear main, rear cover, oil pressure sensor, camshaft sensor, or even the oil pan gasket itself, will hit the lip, run sideways and drip from the same place. At least, this is what I have concluded. I tried looking directly at the rear main and it's really tough to see. Perhaps if you use a dye you might be able to see it. In my case, I already replaced the oil pressure and camshaft sensor gaskets, and the oil pan gasket. That seems to leave just one seal for me.
But, I for one, would not be able to conclude anything for you from the pictures.