They may not be physically real in the material sense but they have been reported in all cultures since recorded history. So even if it's just a psychological condition they are real in that sense.
Or it's just a bunch of:
A. Attention seekers
B. Liers
C. People abusing substances
As there is no such things as ghosts there is no need to "debunk" any of the numberous pictures.
It just goes something along the lines of:
Here is a picture. As you can see it shows a ghost..... FAKE.