As soon as a work (graph, writing, image, etc. is created and posted somewhere, including online, it is copyrighted. Copyright lasts until the creator has died and then 70 years has passed. You must get permission to use copyrighted works OR determine if your use falls under "Fair Use" exceptions. NOT ALL EDUCATION USE is FAIR USE!
"Creative Commons helps you legally share your knowledge and creativity to build a more equitable, accessible, innovative world." With Creative Commons (CC), you can license your own work, or others can so that everyone online knows how it can be used. Look for the Creative Commons icons and check out the links to see what the different licenses mean. Please use CC licenses on your own lesson plans, images, videos, etc. to help others.
If a creator gives his/her work a CC0 license then there are not restrictions to using the work (including no need for attribution).