Looks like it might be coming from the exhaust manifold ? I only have a 3 inch smart phone screen its hard to tell. Wash it of with brake clean and run the truck and see if you can find the point of origin.
I would clean it of and run it to see where its coming from . If you have been idling it a lot it could just be diesel slobber
but pete that is seeping from the top of block and the head, looks like. clean it with that white shirt, and get an engine wash at the blue beacon