On a midnight jail tour of an old Adelaide jail with gallows, I took photos into the darkness of a lightless wing through the bars, with an old film type camera, expecting nothing. When developed, along with normal photos of the people I was with, I had two photos of red and purplish spirally whispy things in the blackness, where there was nothing to see, no reflections, or exit lights, or anything but black. I still have the photos. All the photos before and after were perfectly fine, so not a camera or film issue.
Guards in the control room had also reported seeing prisoners in a yard on their cctv, which weren't there according to the guards who were actually there in person.
It is said that ghosts can be seen in isolated places like caves, cemeteries and prisons...