 Photographs made by film exposure usually contain much information which may be crucial long after the photograph was taken.They can readily be digitised by scanning, and then enlarged to show the detail needed for new analysis.For example, controversy has raged for a number of years over the cause of the Tay Bridge disaster of 1879 when a half-mile section of the new bridge collapsed in a storm, taking an express train down into the estuary of the river Tay.