Copyright law is complicated, and it can be difficult to determine if a certain song, image, or video can be used without obtaining the copyright holder’s permission. I’ve come across an interesting site that does a great job at simplifying the process of determining if a certain work is covered by copyright or not.
Just drag the slider to the appropriate publication date (of course, you need to know this…) and it will tell you whether permission is required and what the copyright status is. Very slick. See it here.