The present hardly exists, after all-it becomes the past even as it happens. A tricky medium, time - and central to the concerns of fiction.
Equally, we require a collective past - hence the endless reinterpretations of history, frequently to suit the perceptions of the present.
The Photograph is concerned with the power that the past has to interfere with the present: the time bomb in the cupboard.
The past is our ultimate privacy; we pile it up, year by year, decade by decade, it stows itself away, with its perverse random recall system.
We all need a past - that's where our sense of identity comes from.
I'm not an historian but I can get interested-obsessively interested-with any aspect of the past, whether it's palaeontology or archaeology or the very recent past.