When you find an image online, the best practice is to assume that its use is protected by copyright. Some creators (and more every day) are relaxing the protections provided by copyright and intentionally are releasing their work under open content licenses such as Creative Commons licenses.
This guide page collects some recommended collections and repositories for finding images that are designated for open or educational use. Most are released with Creative Commons licenses. For more information about understanding copyright and licensing, visit this page on our OER guide.
Even if you use an image from one of these free-to-use sites, it's still important to cite your sources and give proper attribution. For more information about citing your sources, check out the Cite Your Sources page of the guide.