Gratisography is a photo blog from a professional photographer. On the homepage of his site, he explains that all photos are free from copyright and can be used in presentations as well as commercial use. The photographer is a very artistic photographer and captures certain moments that allow the audience to become very intrigued. This site would be great for any age student to find pictures that can be included in a presentation. Teacher could also use the photos in their lessons or to spark conversation.
http://www.gratisography.com/