Creative Commons: Using CC Images
Rights-Free Image Repositories
How To Find Creative Commons Images on Flickr
Although geared towards finding images for use in Blackboard, this tutorial provides a good general overview on how to search for CC images in Flickr, and how to note the specific CC license and terms associated with a particular image.
How to Find Reusable Images on Google Image Search
Although a bit long, this tutorial does a good job demonstrating how to find reusable images using the advanced search feature of Google Image Search. Please note that you still have to evaluabe each image individually to verify the appropriate license. Get more information.