The following attempts to clarify copyright, which often defies clear definition. That said, this guide is not legal advice nor intended to replace legal advice; rather, it is for educational purposes only.
Copyright provides the creator of an original work--a creation that has a modicum of creativity and is in a tangible medium--five exclusive rights over that work:
The right to:
Any use of the creation by someone other than the copyright holder that falls in any of these five criteria infringes copyright.
Copyright is granted automatically: one does not have to apply for or have a copyright notice. One secures copyright merely by creating something that has a modicum of creativity and is in a tangible medium.
Copyright law protects any original work--any work that has at least a modicum of creativity and that has been fixed in a tangible medium of expression. These copyright-protected works can include writing (both fiction and non-fiction), art, music, choreography, movies, television shows, images, and other audiovisual works. Computer programs, sound recordings, and architecture may be copyrighted. And the tangible medium of expression may include paper, canvas, a website, or any other medium in which the work can be communicated or perceived.
The following is not copyrighted and therefore can be freely copied, used, and distributed:
Public Domain: the public domain is comprised of all creative works that are not copyrighted: i.e. works whose copyright has expired (e.g. Shakespeare's works), been waived or forfeited (e.g. works labeled CC0), or works for which copyright was inapplicable (e.g. government works). Works in the public domain can be freely copied, used, and distributed.
However, a reproduction created after 1925 of a work that is in the public domain is copyrighted, unless the reproduction is merely a slavish / artless reproduction--a reproduction without creativity that merely reproduces the original without enhancing or adding to it. In other words, if I take a basic picture of the Mona Lisa that merely reproduces the painting--say, straight on, standard lighting, etc.--then my picture is not copyrighted because it shows no creativity. But if I photograph the Mona Lisa artfully, perhaps by using special lighting, odd angles, etc., then that photograph may very well be copyrighted.