Photographing a nation in motion

The crack in the famous "cracked plate" photograph of Abraham Lincoln appears to be a fissure in the paper on which it is printed, a detail not apparent when one looks at reproductions of what is one of the most famous and evocative portraits of the 16th president. Alexander Gardner made the image only weeks before Lincoln was assassinated, but before the photographer could make multiple prints from the fragile negative, it broke, so only a single photograph was made before the glass original wa...