Public domain is the huge ether out there. Public domain comprises all the works that are either no longer protected by copyright or they never were protected by copyright. It should not be confused with the mere fact that the work is publicly available, such as information in books or periodicals or content on the Internet. Essentially, all the works first published in the United States before 1923 are considered to be in the public domain in the United States, meaning that anyone can get access to the work without having to obtain authorization from the owner of the copyright.
Now, the public domain also extends to the works published between 1923 and 1963 in which copyright registrations were not renewed. All materials created since 1989, except those created by the U.S. federal government, are presumably protected by copyright. As a result, the chances are high that the materials of greatest interest to students and faculty are not in the public domain. In addition, you must also consider other forms of legal protection, such as trademark and patent protection before you use third-party content.
The public domain comprises generic information such as facts, numbers, and ideas, and number two, works whose copyright have lapsed over time or whose copyright holders have failed to renew a registration requirement that applies to work created before 1978. In the third place, you have works published before March 1989 that includes the proper notice of copyright. In the fourth place, works created by the U.S. federal government because, remember, the federal government uses the taxpayers’ money, and so it belongs to the public domain. In rare instances, the owner of the copyright may dedicate works to the public domain.