The very meaning and significance of the word "ghost" has changed tremendously over time. So much so, that on average the word has no real meaning at present. The ghosts of non-Western cultures are unrecognizably different from the standard ghosts of US movies and TV. It is no exaggeration to say that ghosts in the US and England are entirely a creation of the media, like UFOs... indeed, ghosts are a kind of indoor version of a UFO.  Anything perceived as in any way unusual, inside a house, is declared to be the work of a "ghost," whatever that is.  Also, like UFO abductions, many ghost sightings seem to be vivid dreams. It should be no surprise then that the history of ghost photographs is as old as photography itself. The myth is far more deathless than the ghost itself.

Instead of looking for ghosts, why not just listen? As discovered by Sarah Estep in the 1970s all you need is a consumer-grade audio recorder. Just record an empty room and play back at full volume, listen to the noise, and find patterns. You can hear not only ghosts but also angels and space aliens, according to her. You can also use video recordings of TV channels not occupied by TV stations. And much, much more.