The following sources can be searched for free and are public domain or creative commons images. Check them out!
Just because it is easy to find images online, does not mean you are free to use them however you want. A lot of images are protected by copyright - and all images you use in projects should be cited.
It's fast and easy to use a Google Image Search, but many images are protected by Copyright. Click on "Tools" > "Usage Rights" > and "Labeled for reuse" to limit your search results to images that are free to use and share.