The public domain images used in the Basic and Add-on sets were found on the following sites:

	Wikimedia Commons
	NASA Image eXchange
	USDA Agricultural Research Service Image Library
	FEMA Photo Library
	United States Coast Guard Gallery
	BurningWell.org
	AIWAZ.NET
	PD Photo
	Public Domain Photos 8
	Public-Domain-Photos.com
	FreePhotos.lu
	FreePhotos.se