Yeah, first time I saw him was out near Dragon's Bridge. I lost him as I got distracted by a dragon. I just happened to be passing by Hamvir's Rest last night and saw the ghost in the yard. just standing there. It did have an option to talk to him but he didn't respond.
As for the skull, I did that. I picked up one from the dead skeletons and held it there as I took the picture
Second time I saw him on another character, was on the road outside of Whiterun (west of it near Greenspring Hollow) at night. I trailed him down the road to Hamvir's Rest but he disappeared. I might have to take that character back and see if he's there again.
I've never seen a Philter's of Phantom. Where can I find one? I wonder if the shout to become etheral would work?