This photo is from the Smithsonian Institution's photostream on flickr. The Smithsonian has joined the Library of Congress in making available some of its vast collections of images in taggable sets. The intro page is here. A post on the subject on the flickr blog is here. The flickr inititative by which public institutions post their photos is called The Commons. The other two participants in the project are the Powerhouse Museum and the Brooklyn Museum.
The description line for this photo says the subjects are unidentified. It's from the National Postal Museum collection and shows a rural free delivery post carrier using a two-wheel horse drawn mail cart.
The curator who wrote the description says the carrier is a man The person with reins in hand looks like a woman to me. So maybe the other person is the one they mean. Or, maybe I'm wrong about the sex of the driver.
I like how this photo is nicely unlike other documentary shots of its time. It was taken in 1905, when photo subjects still tended to be stony-faced, yet this group is pretty cheerful. I like how the horse is observing the camera along with the people. And I like to think that the driver is a woman.
My son told me about the Smithsonian photos on flickr. Thanks to him!