Section 110(1) of the Copyright Act allows instructors and students to perform or display a copyrighted work without seeking permission of the copyright owner, in the course of face-to-face teaching activities at a nonprofit educational institution in a classroom or similar place devoted to instruction. There are no restrictions on the type or length of work for this purpose. This means you can show a full-length movie, play a full recording of a song, or show any image without a license as long as it's within the classroom.
However, 110(1) does not allow for the making of copies of copyrighted works in the classroom. Fair use (Section 107) is the exemption in the law that allows for “reproduction in copies…for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship or research…” (emphasis added). Please see our page on fair use for more information.