Works in the public domain are no longer protected by copyright and can be freely used by the public. Works often become pubic domain because the copyright on the original work has expired or the creator decided to forgo copyrights and place the work in public domain, free of restrictions.
Creative Commons offers licensing agreements that allow creators to place their works in the public domain or waive their copyrights. For more information about the Creative Commons organization and their work, visit the Scholarly Communication LibGuide.
Creative Commons offers two public domain options. The CC0 license can be used if a creator wants to waive all interests and rights worldwide. This license ensures the copyrights that you have in jurisdictions outside of the U.S. are waived too. The public domain mark is for works that are free of known copyright restrictions, but other jurisdictions may have other restrictions.
According to chapter 3 of the Copyright Law, for works created on or after January 1, 1978 copyright lasts the lifetime of the author, plus 70 years. The earliest any of these works could enter public domain is in 2048.
For works created before January 1, 1978 duration of copyright depends on several factors. As a rule of thumb, works created before 1923 are in the public domain. However its best to double check for any restrictions before using a work.