A very good turn out heard Brian Hawes tell of the progress in U.S. Photo Reconnaissance since the end of WW2. Early information was gained by use of existing military aircraft, but the range and altitude was limited. In May 1960 the world became aware of the U2 aircraft when one was shot down by the Soviets.
From the U2 to some of the latest satellites, Brian detailed Photo methods and equipment. The earliest satellites using film were limited by the fact that the film had to be recovered from space and developed before intelligence could be gained. Once the film was used up, the satellite was allowed to burn up by falling to earth since it could not be reloaded! The advent of digital photography meant better photographs and near instant recovery of images.
While most of the information appears to be Top Secret, in fact, it has now been downgraded and is even being published in a Haynes Manual!