If you are limiting the display of a copyrighted image only to a certain number of students and only to demonstrate a particular concept in class, in most cases, it is permissible to use a copyrighted image in a lecture. However, the same thing may not be true if you are teaching a Massive Open Online Course (MOOC) or lecture open to non-Penn students, if the material needs to be available for a significant amount of time, or if the material is placed in a publicly available website. For more guidance on specifics of use of copyrighted materials in teaching, please consult guides.library.upenn.edu/copyright/teaching