Painters, photographers, graphics designers, filmmakers, musicians, composers, and writers rely on the sale of their creative work to earn a living. There is a system in place to make sure authors get paid and get credit when their intellectual property is used or copied by someone else. Look for the copyright symbol © at the beginning or end of a printed work, or on the title screen of a media production for information about the copyright owner.
Copyright law exists to provide legal protection for the creator and the work.
Examples of copyrightable works include:
Something doesn’t have to be published to have copyright protection. When any form of intellectual property is distributed without the permission of the copyright owner, depriving the owner of the opportunity to profit from the reproduction of the work, the law is being broken.
Some forms of expression are not covered by copyright law and are considered to be in the “Public Domain”. These include works that are either ineligible for copyright protection, or with expired copyrights. All works published before 1923, works of the United States Government, or the underlying idea that is expressed or manifested in the creation of a work are considered to be in the public domain, and thus free of copyright restrictions.
For more copyright basics, see the U.S. Copyright brochure (PDF).
Only one thing is impossible for God: To find any sense in any copyright law on the planet. ~Mark Twain