Unfortunately, black and white photos are so easy to fake...and this is a poor amateur attempt at making ghosts in a picture.
The majority of the floating faces are done through a process of picture developing called 'masking'.
The entire photographic paper is covered except for the portion that you wish to burn an image onto.
To get the misty smokey look, you just move the paper so that any image being burnt onto it becomes blurred. To get a mist, transparent face you just don't give it the full amount of exposure time.
Then, after all that is done, you finally uncover the whole piece of paper and expose the full genuine image.
Voila...
so easy it's boring..