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Photography pioneers' work goes on display in Washington

18 June 2013 Last updated at 21:17 BST

In today's era of cell phone cameras and instant snap shots, it's hard to imagine a time when photography was difficult, technical and time consuming.

But in the mid-19th Century it was confined to a few pioneers. In the United States, they included the brothers Henry and Charles Meade, the subjects of a new exhibition at the National Portrait Gallery in Washington.

Jane O'Brien reports.