The work of Alfred Stieglitz, whose work spanned the 19th to the mid-20th centuries, was instrumental in developing in America the notion of photography as art. Stieglitz pioneered the genre that would become known as "street photography", finding his way around the technical problems surrounding taking pictures in low light, poor weather, and other conditions/problems outside the strict confines of studio photography.
(7/22/13) Update: Well this is embarrassing, another video taken down. Didn't think this one was a problem, isn't PBS the Public Broadcasting Service? Oh well, not to worry, you can still see the video on YouTube here. Enjoy and learn. -RJ.