“Spirit photographs” created by hoaxer William Hope in 1919.

From left: Mr. and Mrs. Gibson with their deceased son; Mrs. Longcake with her dead sister-in-law; the Rev. Charles Tweedale and his wife, with her father.

Arthur Conan Doyle (below, center) defended Hope even when skeptic Harry Price had shown that he was manipulating his plates. “The credulity of dupes,” wrote Edmund Burke, “is as inexhaustible as the invention of knaves.”