Many people are confused by online materials that are said to be “copyright-free” or “public domain.” If an image, song or document is marked “copyright-free,” that simply means that you don’t need to ask for permission to use it. It does not mean that you don’t have to cite the source, however – citation is a means for providing access to the source and for indicating that you used that source to support your own argument or findings. If you use a political cartoon, a graph, a photo, etc. without providing a citation, it's plagiarism.
Many online items, particularly images, are created under a "Creative Commons" license. You may run across this as you research a topic. Creative Commons licenses allow authors, artists, teachers, etc. to create new works (photographs, essays, lesson plans, you name it) and decide how much they are willing to share with the world at large. A good place to find images for your PowerPoint projects is Flickr, where Creative Commons licenses are often found. Don't forget, though: the license simply allows you to use the image without asking for permission. You still have to cite it in order to give credit to the author.
Fair use" is a type of permission for using copyrighted works. Schools often claim that anything can be used under Fair Use guidelines but this is not always the case. For an entertaining and informative explanation of aspects of copyright and fair use, you can watch the 10 minute video in the box below.
Here's an interesting video that's not only about copyright and fair use, but illustrates how one can create something new within the boundaries of copyright law.
Are you looking for images to use in your presentation? Try these sites: