I'm sorry, no disrespect intended, but I found this part of the article hilarious:
Spiritual photography has its roots dating to the 1860s.
William Mumler, a Boston and New York photographer whose works had ghostly images appearing in the background, was the first known practitioner of the craft. His patrons included Mary Todd Lincoln, who visited him after her husbands assassination.
The mayor of New York ordered an investigation into his practices, and P.T. Barnum testified for the prosecution at his trial in 1869. Mr. Mumler was acquitted but also discredited after being suspected of manipulating photo plates.
:hilarious::hilarious::hilarious: Why was he prosecuted? For having ghosts in his images? And why is the head of a circus a prosecution witness???