Lol !
Ive seen so many of my own photos with unexplained/unwanted marks on them for whatever reason, by pure random nature eventually someone is going to see something in it. its like looking at the clouds, if you look long enough you'l see one that looks like something.
if its unexplained then its unexplained its as simple as that.
that doesn't mean that the explanation is a ghost.
it could be something as simple as light shining on the lens but the light itself is out of view. you are guaranteed to get this effect if you take a picture into the sun without a suitable shroud to keep the sun off the lens. any marks on the lens at all will cause the image to be affected let alone lens flair which is often used in artistic effect in films/photographs even PC games - thats actually caused by the same thing but internal total refraction causes the light to form a much clearer image.
however it is interesting, just like those funny shaped vegetables that resemble famous people.