Use this to search for images that are in the public domain. To do this, scroll to the bottom and select from the Usage Rights drop down menu "free to use and share" or "Free to use, share and modify."
Copyright friendly images
Go here for more information on copyright, public domain, and creative commons.
Even if it's "free," you should give credit to your source.
Creative Commons is a nonprofit organization that works to increase the amount of creativity (cultural, educational, and scientific content) available in “the commons” — the body of work that is available to the public for free and legal sharing, use, repurposing, and remixing.
Pics4Learning is a copyright-friendly image library for teachers and students. The Pics4Learning collection consists of thousands of images that have been donated by students, teachers, and amateur photographers.
More than 100,000 drawings, photographs, paintings, and advertisements available to the world under Creative Commons licensing. The images available through the Wellcome Images library are primarily of a historic nature.
Allows you download and re-use low-resolution images without restriction. To download and re-use high-resolution images you need to publish a credit to the creator of the image. That's not a hard requirement to meet. To help you meet the requirement of crediting the photographer, FreeDigitalPhots.net offers a simple chart that outlines how to credit the creator of an image. The left side of the chart lists the ways the images can be used and how to credit the photographer for each use case.
Houses thousands of images that you and your students can re-use. Searching in the Wikimedia Commons isn't the most intuitive process. Search the Wikimedia Commons by keyword or browse it by category and topic.