The BBC has put up an audio slide show on its Web site, showing many of the most important reconnaissance photographs of World War II, with two experts discussing why they're important and what they reveal.
It's a fascinating look at how intelligence was gathered in those days, and a sobering reminder of what our fathers and grandfathers went through.
showing smoke from the crematorium chimneys on the left
It's only a little over 5 minutes long. Highly recommended viewing - and listening.