While doing research on different ID projects of mine - Japanese ord, ADSIDS, CW, etc. - I did about 5-6 week long trips to the national archives - spread over several years. Three laptops, three scanners, eight hours a day. All I would do was identify the photos I wanted, my sherpas (wife, son, collecting buddy) would run the scanners till they burnt out. All scans were done at 600 or 900 ppi, so I got the best resolution possible. Ended up with several thousand great images, but many too technical/dry for this thread. As I find time I hop through some of the files, looking for shots involving soldiers or a mixture of items that may interest the greatest number of members.
I do pick up original photos when I find them, there are several hundred in the library, but many still need to be catalogued and can be difficult to find when I am looking for them.