How can you tell if something is/ is not protected?
While it can be a challenge, many times all you have to do is examine closely the work itself (or where you found the work) for a notice of copyright ownership. For example, look for the “Terms of Use,” “License Information,” or “Legal Agreement” section of any website. Some sites have an FAQ page that will answer the question of how to properly use the work they are providing. Note: Just because there might not be a copyright symbol visible, it does not mean the work is not protected. It is no longer required to publicly state whether a work is copyrighted.
There are many types of works not protected by legal restrictions on use like those that have passed or been placed into Public Domain. Other works which retain copyright protection, but which allow some use without permission, include those offered Royalty Free and those in which a "fair use" argument can be made.