This started as a project among edubloggers and has now expanded beyond the original 50 who started it. It is an excellent example of what could be done as a classroom assignment- having students photograph something relevant to your content matter and upload it to a Flickr site. Being a Flckr site, discussion is available.
The World Digital Library provides free access to manuscripts, rare books, maps, photographs, and other important cultural documents from all countries and cultures, in Arabic, Chinese, English, French, Portuguese, Russian and Spanish.
This site has the most information of any of the sites I found. In addition to text and photographs, there are also videos, lesson plans, and information about the scientists who study the biomes.