Snapshots of the American Civil War

This year marks 150 years since the Battle of Gettysburg, perhaps the most important - and certainly the bloodiest - battle of the American Civil War.

Coinciding with that anniversary the Metropolitan Museum of Art in New York is staging a landmark exhibition of what are being described as ''the finest and most poignant'' photographs from these cataclysmic four years in which an estimated 750,000 Americans lost their lives.

The Met's chief curator of photography, Jeff Rosenheim, has also written a book - Photography and the American Civil War - to accompany the show.

He's been speaking to Michael Maher.