Flickr contains millions of photographs shared by Flickr users under Creative Commons licenses, and is a strong source for contemporary travel, nature, people, and design photographs.
Several overlays to Flickr offer enhanced search functionality and additional features.
You are free to use images from these sources in papers, presentations, multimedia projects, websites, blogs, and portfolios that are open and available to the public. When you use these images, you do not need to restrict access to your class or academic environment.
Always read and comply with the use restrictions for specific image sources. Always cite images someone else created.
These sites offer at least some images for free general use. These sites also contain advertising and/or offer images for sale.
Read each site's conditions for use carefully. Different images from the same site may have different use restrictions, too. Make sure you know what they are.