Hi Scott,
We had a similar discussion recently under a post entitled 'spooky towel man', but the photograph I took seems to be out of action, so I have reposted it again here for you. This was taken using a mobile phone and has no post alterations to it whatsoever- it is as it was when taken.
Try feathering the edges of you 'ghost' and duplicate the background layer then place it back on top of the ghost (so it's in the middle) and then bring down the opacity, that might make it look more natural. Also, try and make the ghost the same quality/resolution as the surrounding!
It's a great picture though, made me laugh!
OK, for some reason my image will not display, I will try and post it again later.
Regards,
Robb