Item Favoring Fair Use
No similar product marketed by the copyright holder
Explanation
If your students are having difficulty understanding a chapter of a textbook, you might decide to put together a PowerPoint presentation over the material in which you lift photographs from the textbook. Using those images might be fair use unless the textbook publisher sells PowerPoint presentations over the textbook chapters. If such a PowerPoint presentation does exist, it would be difficult to argue that creating your own presentation constitutes fair use.
If you created a series of PowerPoint presentations over a textbook so that your students would not have to purchase the textbook, your PowerPoints would not be fair use even if a similar product did not exist.
