Determining whether or not a work is protected requires consideration of many factors. The following site can be used to determine if a work is still protected by copyright:
Copyright Term and the Public Domain in the United States - Cornell University.
This detailed chart addresses multiple variables for determining copyright duration for U.S. works.
Copyright is a form of United States intellectual property law that affords creators certain exclusive rights over their works for a limited period of time. Protection of these rights is automatic and does not require formal registration - although registration can be beneficial to the copyright holder in cases of infringement (i.e. copyright violation.)
What is protected?
Works that are original (not copies of others), display a minimum degree of creativity (unlike a simple A-Z list), and are recorded or "fixed in a tangible medium" (e.g. saved in a computer, painted on canvas, written on napkin in the cafeteria) are automatically protected under copyright.
Copyright is frequently associated with literary, pictorial, motion picture and musical works. However, research papers, computer code, and some figures used in the STEM disciplines meet the criteria for copyright and are therefore protected.
What is not protected?
Facts, ideas, concepts, principles or discoveries are not own-able under U.S. intellectual property law. Processes, procedures, methods and systems are not protected under copyright, but may be protected under U.S. patent law. Works that are in the public domain which includes works by the U.S. government and works for which copyright has expired are not protected.
Who holds the copyright to a work?
Creators can include authors, photographers, composers, artists, cartographers and architects. These creators can transfer or license some or all of their copyrights. In the case of "work for hire" the employer, not the creator holds the copyright for the work - although the creator may retain some limited rights to the work.
What are the exclusive rights?
Copy - right to reproduce the work (whole or in part.)
Make derivatives - right to create translations, sequels, adaptations, other works based upon the original
Distribute - right to make the work publicly available through sale, loan or gift
Perform or display - right to publicly show or perform the work.
Permission - right to grant permission for any of the aforementioned.
How long are works protected?
Copyright duration varies depending on when a work was created, who created it, whether or not it was ever published, and in some cases, the work's registration status with the Copyright Office. In the United States, works published since 1924 may still be protected by copyright. Works created since 1989 are be protected for 70 years after the death of the creator (or death of the last surviving creator in cases of joint authorship.) In the case of corporate authorship, the work can be protected for 95 to 120 years.