There is now so much photo and image content available under remixable CC licenses that it is probably fair to say that you can now find almost anything you can imagine to use in your school project, blog, or presentation, provided you follow the conditions of the applicable license used.
Dig in and find some for yourself!
Remixable Flickr Photo Samples
Remixable Picasa Photo Samples
You can search for remixable photos yourself using the links below: