Above is a pic of what I believe is a ghost.  I was taking a picture inside Southsea Castle (in Hampshire), August 2009, of something and my camera failed on me, somewhat annoying as I hadn't finished taking pictures in the castle. When I got the picture home it was black so using Picasa editing software I lightened up the image and got what I believe is the monk that I later found out allegedly haunts the castle.

Alas the only other person with me was my girlfriend and she photographed nothing of interest. The picture, however good, does not prove I took a good picture of a ghost merely a picture of something. I cannot prove the picture is that of another human and only my word exists that we were the only 2 people in the area. It's certainly not a picture of myself or my girlfriend. I am at a loss to explain it despite returning to the castle to see if I could replicate the image. It's not a mannequin, re-enactor or even a real life monk!

I'd appreciate any help anyone can give me to explain the picture however I can assure you that I have tried the common sense approaches first already!