Creative Commons: Search engine for open source images, audio, and video.
flickrCC: This section of Flickr offers images that are available under a Creative Commons license and also explains the different types of Creative Commons licenses.
Google Images: While not all images on Google Images are Creative Commons licensed, it is possible to limit your search results to only images available under a Creative Commons license. To do so, run your search in the standard Google Image search bar and then on the results page, click on the "Search Tools" button just below the search box. Another drop down menu will appear with "Usage Rights" as an option.
Multicolr Search Lab: This tool from TinEye allows you to search for Creative Commons-licensed images by colour.
MorgueFile: As macabre as this sounds, it's merely a free photo archive. No dead bodies here!
