Another treasure off the Project Gutenberg feed: Photographic Amusements (circa. 1896).  Think of it as a turn of the century guide to photographic special effects.  But please remember:

As Mr. Woodbury stated in his introduction to the original edition of this book, in order to avoid misunderstanding, it would be well to explain at the outset that it is not intended as an instruction book in the art of photography in any sense of the word. It is assumed that the reader has already mastered the technical difficulties of photographic practice and is able to make a good negative or print.

Subjects include magic photographs, spirit photography, electric photographs, distorted images, freak pictures by successive exposures, and many others.  I was drawn to the spirits.  Here are the photo’s used as examples, and a link to read more about it.

Not the scariest of images, but interesting reading.