You might not have heard, but Google has links to the digitized photo archives from Life magazine, including a lot of pictures that were never published. If you go to the Google home page, you can click on the Image search tab and currently, there are links to some possible searches of the Life photo archives, including World's Fairs and Marilyn Monroe. You can also click on the link and see some searches by decades, ranging from the 1860s (U.S. Civil War) through the 1970s. Or you can just do a generic image search and add "source:life" to the search string, and it will look only in the Life archives.
I find the older pictures to be especially fascinating. Seeing President Lincoln standing in front of a tent at Antietam in 1862 or Red Cross founder Clara Barton seated next to an ornate clock, wearing a dress with a hoop skirt several feet in diameter, is a window on another time. The people were like us in many ways, but their lives were very different. Technology changes the way we live, but not who we are.
The amazing thing, when you think about it, is how brief our "modern" period really has been. Automobiles, for instance, have only been around and in common use for about a century. My father is 70 years old, and has been around for about 70% of the era of the car. His father was born in 1911, at a time when the horse was still the main mode of transportation for most people; if they were going to travel long distances, it would be by train. Within his lifetime, Man walked on the Moon and sent probes to other planets in the solar system, most people owned automobiles and had flown on airplanes for long-distance trips.
And yet, our photographic archives only go back a century and a half. We have photographs of Lincoln and all subsequent American presidents, but if you want to see what George Washington looked like, you have to depend on the skills of portrait artists. So if you, like me, find the old pictures interesting, feel free to sift through those vintage images of the past.