Copyright symbol, by OpenIcons, CC 0
You may use copyrighted images in your assignments without obtaining permission when your use meets all three of these criteria:
The use is:
You still need to provide a citation for all images used.
Creative Expressions in a Fixed Form
Copyright is a form of protection provided by U.S. law to authors of “original works of authorship,” including “pictorial, graphic, and sculptural works.”
The owner of copyright in a work has the exclusive right to:
Anyone wishing to use the work in these ways must have the permission of copyright owner.