You can add links here to environmental photo databases here.
Visible Earth is NASA's database of photos for the earth.
Blue Earth Alliance attempts to raise awareness of our chaning planet through photography. They have a number of current and archived projects containing beautiful imagery of our Earth.
Yann Arthus Betrand is a French photography who takes areal photographs of the Earth. Many of these photos show various ecosystems, geological formations and way in which humans are changing the face of planet Earth.

Huge database, but most of the photos have strong copyright restrictions. "CalPhotos is a collection of 168,403 photos of plants, animals, fossils, people, and landscapes from around the world. A variety of organizations and individuals have contributed photographs to CalPhotos. Please be aware that these various contributors maintain copyright and follow the usage guidelines provided with each image."
This database has 657 photos of environmental and farming interests. The photos are worldwide and seem professional. Open use for class. "Welcome to the LEAD Photo Gallery. The purpose of the Photo Gallery is to illustrate the Livestock, Environment and Development interactions across the globe. The photographs are classified and available to download with an average resolution (maximum length of 600 pixels) in JPEG format. To obtain the original photographs at a better resolution please contact, by specifying the reference of the photograph, and the intended use."