Some of the most iconic images of the 19th and 20th centuries were captured by Life photographers. Now those images plus images never published are available through the Life Photo Archive hosted by Google. Last month Time and Getty announced the creation of Life.com. Life.com is not live yet, but the Life Photo Archive on Google is great step in making high quality iconic images available online.
Applications for Education
The Life Photo Archive could be a great place to get images to introduce a historical topic or spark a conversation about an event in history. The images from the archive might also be of interest to photography teachers as teaching models.
A couple of other places to find high quality images are the Flickr Commons and Archives.gov