I took this photo in St Andrews, Scotland in 2008. It was taken underneath a ruined castle.
You can see the profile of a person facing right.
In 1546, the garrison of Scottish Protestants was besieged by Scottish Catholics. The attackers attempted to mine under the castle. The defenders created a countermine to stop the attackers, which is where this photo was taken.
The apparition can be nothing other than the persistent impression, stuck in time, of a poor soul swept up in an ideological conflict that took everything from him.