Exposure accidents can produce images that are far more interesting than properly exposed shots. My father double exposed the Parthenon when we visited it in August of 1969. I am sure this was not what he intended but the resulting superposition of times makes you look twice. When tourists visit ancient sites they are indulging in a bit of imaginary time travel. This double exposure of instants separated by a handful of seconds is of no great value but imagine a camera that could double expose the present with what you could see from this very spot when the Parthenon was first built. The resulting image would instantly become the most valuable photograph ever taken.