Behold is a search engine that helps you and your students to easily find images that can be used on your website, in your newsletters, and with classroom projects or lessons without fear of violating copyright law. Behold searches for images in Flickr.com that are licensed under Creative Commons. The Creative Commons license grants use of an image with some restrictions or requirements (which you need to carefully read with each image you use).
A great feature of Behold is that it also helps you to pinpoint the type of image that you require. For example, when searching for "beetles" you may get images of insects or cars. But Behold's interface allows you to use a drop-down menu to choose the category of images that best meets your needs.
Thanks to http://www.freetech4teachers.com/ for sharing this great resource.