Paris Catacombs Ghost Picture

Agnes sent us this fascinating ghost picture taken in the Paris Catacombs:

"We were visiting the Paris, France catacombs, Sept. '07 with a private guide. There were only three of us: me, my friend (in the pic), and the guide. My friend took a picture of herself for fun and ended up with this. Needless to say, there was no smoking, no high humidity - we were above the underground, and no tricky photoshop from us. However, I cannot understand if this is a ghost, why it was so close to her. The French catacombs are not known to be haunted (according to my research on the web); however as the guide told us, and this can be confirmed on the Internet, many Parisians were buried until the 18th century there, because of the Black plague. People were afraid of getting the plague, and were not often offered a sepulchre, or a proper ceremony."

Could the appearance be due to the vast amount of human bones which line the Paris Catacombs?  Is it a ghost, an earthbound spirit from the days of the Black Plague that ravaged much of Europe?  You decide...