Here's a posting to print-pubs-l that Mary Ann alerted me to...thanks! 
"Many tourist bureaus throughout the U.S., including the Washington  
Convention and Visitor's Bureau, have Websites or CDs available with photos
of buildings and sites in their state. In the case of the Washington
Bureau, anyone can use the images as long as the Washington Convention and
Visitor's Bureau (WC&VB) is given credit. Among the listings for other free
sources:   http://www.firstgov.gov/Topics/Graphics_State.shtml 
links to many individual state and local government sources including DC, the Convention & Tourism Corporation pressroom page, 
http://www.washington.org/index.cfm?blnNavView=True 
where 300 dpi jpeg downloads may be accessed directly by post or clients 
upon registration from any country in the world. . . . . "
