Creative Commons is a non-profit organization dedicated to "the sharing and use of creativity and knowledge through free legal tools". They aim to expand the amount of open access content (images, texts, videos, music, etc.) available on the internet by encouraging creators to share their work with the public, allowing for reuse, repurposing, or remixing of the material.
Creators are provided with different licenses that enable varying levels of use. When using Creative Commons material, you must make sure to provide the appropriate type of attribution.
These sources are great for finding public domain icons and clip art.
Most images found online are subject to copyright restrictions and should not be legally used without permission. There are, however, many open access sources for images that are openly available to the public and can be used for projects or presentations.
Consult the sources found on this guide for your images, but remember to pay attention to any restrictions found in individual sources. Generally, you will need to cite the original image in your work.
Flickr is a popular photo sharing site containing millions of Creative Commons-licensed images. There are many tools available for locating those images amongst the larger collection.
These websites provide free stock images and other photographs. Most of these sources contain images for sale, or contain advertisements, so pay attention to the different categories as your search/browse.