This page lists some Internet resources where travel-related images compatible with our copyleft can be found.
Mav's images. Maveric149 says, "I have a couple hundred images of various national parks and other things in the western part of the United States. Anybody can use them under terms of either the GNU FDL or CC-Att/SA." (see dual licensing for more info on dual-licensed works)
Chris Croome's images. From Chris's user page: "I have loads of holiday photos that are available under the Creative Commons Share Alike License feel free to use them to illustrate this site!"
PD Photo. Several thousand images, all in the public domain. Very nice quality, too.
OpenPhoto.net. A repository of more than 22,000 photographs available under the Creative Commons Attribution license. (This is compatible with our copyleft, as long as we copy over the attribution, too.)
Gimp-savvy.com. Public domain photographs from the US Government, arranged and catalogued by volunteers.
Buzznet has loads of stuff released under its default licence, which is the same as ours.