If you had to file this photograph in an archive and select keywords to describe it, what would you say? In this shot from the Library of Congress's Flickr photostream (selected more or less randomly, because I love her smile and her trumpet), we might start with "Rose Sanderson" printed at the top of the frame. Is Rose the smiling trumpeter? Her appearance in the center of the frame suggests so, but we can't know for sure without further investigation. And what of the other women? What is the occasion for gathering together with smiles and trumpet? And where exactly was the photo made? One of the banners seems to say "Votes for Women." So maybe this is some sort of suffrage parade or gathering, which puts the photo before 1920, but we don't know where, or exactly when. There appears to be a date scrawled on the right side, but it is difficult to read.
Then there's an entirely different way we might describe the photo: moving beyond the photograph's content to consider its status as an object. What sort of camera made it? What does the negative look like? What is its size?
The question, "What is this a picture of?" is never easy to answer. I have written about this in the context of my work as a researcher in photographic archives. But it's useful to get the archivists' take on things as well. The Bigger Picture blog from the Smithsonian offers a great post on how archivists use descriptive metadata to make it easier for folks like me to find what I'm looking for. Marguerite Roby walks us through the various choices archivists make as they seek to make visual information accessible to as many users as possible.
As for "Rose Sanderson," well, that may not even be her name. See here for how Flickr users have had fun working through the archival mysteries in this photo.
(Check out also a related Bigger Picture post from Roby, called "What Does a Photograph Archivist Do?")