Many ghost believers state that ghosts appear on film or video recordings. A camera can be a quite useful scientific instrument, in that it records the actual appearance of an object, getting around the perception and memory errors of human observation.
There are vastly more cameras around now than previously, yet numbers of reported photos of ghosts have declined. This is true as well of UFOs, fairies, witches on brooms, angels, Nessie, Ogopogo, Bigfoot, Midlands Melanistic Panthers, and other cryptids. With more observers capable of making recordings, if there is anything observable there, the number of recorded observations should increase.