Attached Link: http://www.fws.gov/help/policies.html#num2

Interesting site. It does say public domain images. It also says, "When using these images, please credit the photographer and the Fish and Wildlife Service. Ex. John Doe/USFWS. March 14, 2003 was the centennial anniversary of the National Wildlife Refuge System." They do say on another page that not all the images are copyright free so that's worth paying attention to. And they say : Copyright Unless otherwise indicated, resources in the National Image Library are in the public domain. No restrictions or copyrights are placed upon these materials. You may credit the source of the resource using the information contained in the "Creator" or "Rights" field of the resource record. For more information, see USFWS policies. Thanks for the site.