There are a lot of sites on the net that have ghost photographs.  Some are pretty convincing and some are not.  The easiest and best way to analyze a ghost photograph is to look at it very closely.  Generally speaking a photograph of a real ghost will be fuzzy around the edges of the ghost.  If you see anything that clear defined and very easy to make out...it's probably a fake.  This is usually the end result of a double exposure that was done up to show a picture of a "ghost" and whoever did it didn't take the time to do enough dodging and burning on the print.  Anyone with access to a darkroom and knowledge of developing and printing can turn out a "ghost" picture.   It's a simple procedure.  You first expose the background photo on the paper, then you double expose the "ghost" over that and use a shorter exposure time to lighten up the ghost image.  A friend who is a photographer and has a very well equipped darkroom and I have turned a few of these out, but they ended up in the trash can. but we had fun doing them up.