My friend and often co-author, Julie Ferguson, tried out some techniques to make ghostly photos, simply. We share them here -
We tacked up a plastic paint tarp (it was cooler because there was paint smearing it) in a doorway. We put a powerful light with no shade on it behind the person and the photographer was on the other side of the plastic photographing them pressing up against the plastic.
Using an Infrared camera we took shots with mood.
With dim enough lighting and moving super fast while taking the shot, you blur.
Hiding under cheesecloth
Drape cheesecloth over you and wear some pale makeup and clothing.
Pale makeup, circles under the eyes, bluish lips, some cheesecloth and drapy white clothing and a great ghost can be made.
When all else fails, consider the old-fashioned method -