I like looking at old photos, and I wonder about the motivation of the people taking them. Taking photos in the late 19th and early 20th century was much more complicated than it is today. Today, anyone can whip out a cell phone and snap a selfie, and lots of folks do that, but back in the day, a photograph required a knowledgable photographer and big equipment. Let's take this picture, for example.
introduced his Brownie camera in 1900 to make photography available to the masses, I doubt this photo and many others like it were candid shots. I suspect that this group of Rangers wanted this photo for a particular purpose. So, they set it up to record a particular event. I'm sure that many of the men groused about it, but the bosses were firm and the photo was captured. Then, the film was sent to a processor who used chemistry to print the photo on special paper. Photography was difficult in those days.
Today, I simply take my cell phone or my digital camera and in seconds have a photo I can use.. Like my propensity to take a random picture of a goofy dawg to post on Sunday morning.