Flickr is a great source of Creative Commons licensed images that you or your students can use without worrying about breaching copyright. You can find links to some excellent Flickr groups on the links page of this wiki. To help explain Flickr, check out this CommonCraft video on Online Video Sharing.

Not all images on Flickr are Creative Commons licenced, (many are copyrighted and as a result should not be used without permission which can be sought from the author). The following movie may help you search efficiently for Creative Commons licenced images.

You might also like to check out the Using Flickr To Find Images.pdf notes on searching for Flickr images.