IF YOU USE MATERIAL UNDER THE FAIR USE PROVISION
If you want to sleep better at night, you should ask the copyright holder for permission to use his or her work. However, a Fair Use defense does not require that permission be asked or even granted. A copyright holder cannot prevent use that is otherwise Fair Use.
Some sample permissions letters are available from GA Tech library at https://www.library.gatech.edu/reserves/resvletter.htm.
(These are Jim's "common-sense" recommendations only; the above items are not coded in law nor are they official guidelines.)