Usage rights tell the user what they can and cannot legally do with images that they wish to reuse.
A Brief Summary of Types of Usage Rights (from Google Support)
Find more information on this topic at:
Use Creative Commons to look for images that have licenses that fit your use, or to see if you can locate the license for a particular image that you have.
NOTE: You may need to do your image search by License/Usage rights at these sites.
Hover over the title of the resource to get additional information. ALWAYS check images rights and restrictions prior to using an image.