Although there are lots of ways to detect spirits nowadays, back in the sixties (the 1860s, that is), the preferred method of proving the scientific existence of a ghost was the use of the newly invented camera.

Unfortunately, the camera—and the gullible public—are quite easy to fool. At the outset of photography, the photographic plates needed a long exposure time. Which is to say, the person sitting for the picture would need to sit still for quite a while—sometimes up to a half an hour. Let’s say that a photographer is taking a picture of a family. If a stray sheep would enter the field of view for even a minute, traces of that sheep would register on the plate and appear in the picture, before being shooed away. While the family—who sat for the full half-hour—would appear solid, the sheep on the lam would appear blurry, transparent, and ghostly.

Another trick was to pre-expose a photographic plate with some image on it—let’s say, a man wrapped in a sheet. When an unsuspecting person arrived to have their picture taken, the photographer could use the pre-exposed plate. After developing the image, the customer (and duplicitous photographer alike) would gasp and the customer would say something like, “why that sheet resembles my dear Uncle Unctious, who passed away from spotted mountain ennui just last year!”

The idea of seeing spirits in photographs was quite natural to the general public at the time. Due to the long exposure times requiring the subject to sit still, most early cameras were used primarily to document the recently departed still on their deathbed. For spirits to begin appearing in the picture was merely a (super) natural development.

For a more detailed look, Ghosts of the Prairie magazine has more information about spirit photography.

And here is a Gallery of Spirit Photography from the American Photography Museum.

Oh, and the “spirit photograph” which you see here does indeed show real ghost, and not a rumpled paper towel at all. Truly.