Creative Commons (CC) Licenses: enable content creators to allow others to use the work, while reserving some rights.
Platforms that integrate Creative Commons Licensing: make it easy to apply a CC license to your work. Many supply a ready made citation for re-users to copy. Note: Check the rights of each item. Not all items have CC licensing applied.
Creative Commons Search
Google Advanced Image Search: Change the usage rights to "free to use or share" to search for Creative Commons licensed images.