According to US Copyright law, every original work created or published before 1929 is in the Public Domain, meaning it is out of copyright. Exceptions are made for revisions and new editions.
So works created since 1929 are copyrighted. This means that if someone wants to use them must get permission from the copyright holder (author/creator or publisher). Some use may fall into Fair Use, which is very restrictive.
Copyright is not limited to physical items. All content fixed in a tangible medium (including posted on the Internet) is automatically copyrighted.
Please note that resources and materials available free of charge does not mean they are free of copyright. For example, there are millions of videos on YouTube and millions of images on Google Images website. But most of these are copyrighted. That is why both websites have tools that limit their content to those materials that are free of copyright.
Sometimes creators of copyrighted materials decide to offer their works to the public with a few or no restrictions on how they should be used.
To prevent misuse of their works and have documentation needed for possible court cases, creators of copyrighted materials assign Creative Commons licenses to their works on Creative Commons website.
Creative Commons is a non-profit organization that offers licenses to these works free of charge based on restrictions creators put on the use of their works.
Creative Commons issues 6 types of licenses. Sometimes works in the public domain are referred to as having CC license 0.
For online material: Select the license that is appropriate for your material from the CC license chooser and then follow the instructions to include the HTML code. The code will automatically generate a license button and a statement that your material is licensed under a CC license. If you are only licensing part of a work (for example, if you have created a video under a CC license but are using a song under a different license), be sure to clearly mark which parts are under the CC license and which parts are not. The HTML code will also include metadata, which allows the material to be discovered via Creative Commons-enabled search engines.
No. CC offers its licenses, code, and tools to the public free of charge, without obligation. You do not need to register with Creative Commons to apply a CC license to your material; it is legally valid as soon as you apply it to any material you have the legal right to license.
CC does not require or provide any means for creators or other rights holders to register use of a CC license, nor does CC maintain a database of works distributed under Creative Commons licenses. CC also does not require registration of the work with a national copyright agency.