Lord Combomere's Ghost
As with many early photographs, it must be borne in mind that the exposure time was quite considerable: the photographer Sybell Corbett reckoned that the camera was stood unattended for an hour. This, of course, would be plenty of time for someone to come into the room - whether deliberately or inadvertently - and sit in the Lord's chair for several minutes before moving on.
This is the line adopted by most commentary on this famous photograph, but against that, mention must be made that the photographer herself maintained tht the house was empty during the shoot - with the family and staff being present t the Lord's funeral. Members of the family are also said to have identified the figure as that of Lord Combomere which would, if true, be a compelling corroboration.