I'm not sure why people would think that photographic film would pick up anything they human eye couldn't. If anything, the human eye is far superior in its ability to pick up light. What is the supposed mechanism that these ghost figures get transfered to the film, if not by photons being focused onto the film's surface?
The problem is that there is no theory for how such a ghost image could be transferred to the film, but there is much evidence of fraud and accidental double exposures over the years. There was a time when spirit photos were quite fashionable. Remember that there were many people who though for sure the fairie pictures were real too, but it was finally proven, as all skeptics were sure, that they were just simple pranks. So many people are fooled because of their desire to believe.
rem