Update: This is now an e-card:
I would check out Flick.com's Commons. They have lots of photos with "No known copyright restrictions". The Library of Congress collection also has a lot of color photos. I especially like their 1930s-40s in Color and Gardening in Color and Photochrom Travel Views.
Here's a variety:
Valerie (and Chris):
Those are some great pictures to use for "period" postcards for WikiTree Travel events. After all, genealogy and history are handmaidens to each other.
I'm especially drawn to the 1930s-40s in Color collection as it is recent enough and yet not at all boring for the younger sets of eyes. Of course, fitting images into the outlines of a WikiTree logo is another matter.
Good luck! This seems a really good idea for promoting the site(s).
Great work, Valerie. Thanks!
Pretty much every state has a site somewhere with completely free photos.
The one below is of the old train station in Missoula, Montana. The photograph that I grabbed is a very modern color shot. This is what it looks like aged and there is no restriction on its use.
From Big Sky Country - Montana
Thanks again for everyone's input. Here is the end result ...
To send it as an e-card: http://www.wikitree.com/index.php?title=Special:Ecards&p=WikiTree_Images.jpg