Links
Here are a few other resources for royalty-free photographs
Antarctic
Photo Library
Archive of many free Antarctic photograph's from the US
Antarctic Program library.
FreeFoto.com
This site offers a good number of pictures of all
varieties for non-commercial use with very few restrictions.
Copyright Free
Photo Library
While the number of pictures available is low, this
site offers near restriction-free use of their photographs with registration.
U.S. Fish and
Wildlife Service
Many nature-oriented, public domain images available
for download or viewing complete with picture search engine.