Judith,

You might be interested in the work of a Brit named, Harry Oldfield.  Among other things he has demonstrated photographic techniques that capture scenes from the past on digital video and still cameras.

I remember one of his videos showed something white (he claimed it was a little girl) moving along a sidewalk in a very old cemetery.  It responded to his thoughts when Harry asked it not to be afraid, it stopped moving away.

But the really interesting part was that in the background of his cemetery video there were structures, monuments, grave stones, etc. that were not visible to the naked eye.  They were only visible in his video.  When he later visited the office of the cemetery the caretaker showed him photographs of the cemetery taken many, many years ago.  Some of the structures in the old photograph had been removed over the years (don't recall why) but were still visible in Harry's video.

He also had video showing something like a tower near a bridge, or part of the brides somewhere in London that was removed a very long time ago as the bridge was updated over the years.  The tower and scaffolding (if I remember correctly) were visible in his video, but not to the naked eye.

Bruce