Google has made the Life Magazine Image Archive available to the public:
"Search millions of photographs from the LIFE photo archive, stretching from the 1750s to today. Most were never published and are now available for the first time through the joint work of LIFE and Google."
LINK (select Images in top line to get to Life Magazine Image Archive Search.)
Yes, they mean 1750s to today, because the Life Archive actually includes both photos and illustrations. If you search American Revolution, you will find images, and if you search Vietnam War, you will also find images. If you are a star-struck person, you'll love this image archive-- Marilyn Monroe fans will positively flip when they see the huge number of photos from various phases of her career.
A drawback- images are copyrighted, so permission would be needed to reuse in articles, books, websites, etc. But you can save images to use as wallpapers / screen savers / reference photos on your own computer, so give thanks to the people at Life Magazine and the Google poobahs for a real image treasure trove!