No. Copyright does not need to be registered in the U.S. It is automatic as soon as a work is fixed in a medium (written, recorded, etc.).
Any creative works, such as books, poetry, music, art, movies, and plays. Translations and adaptations, as well and databases and software are also granted copyright protections.
What Can Be Copyrighted Infographic by Maggie Swanger is licensed under CC BY 4.0.
The U.S. copyright term lasts for the life of the author plus 70 years.
You can use copyrighted materials without asking permission under certain conditions:
If something is in the public domain, you are allowed to freely use it in its entirety without obtaining permission. Works enter public domain when the copyright term has expired, or if the creator has relinquished their copyright and dedicated their work to free public use. This is the case with some government documents. It is also important to note that ideas and facts cannot be copyrighted, only creative works.
Public Domain Infographic by Maggie Swanger is licensed under CC BY 4.0.
The U.S. Code does not explicitly delineate number of words, lines, notes or images that would constitute fair use or not. Consider the following four factors. If more are in favor of fair use, you can use the material in your class. If most factors fall under "less likely to be fair use" you will want to find an alternative, or reduce the amount you share.
The TEACH Act addresses digital uses of material for online learning. It provides for the performance and display of copyrighted materials for distance education by accredited, non-profit educational institutions (and some government entities) that meet the Act's requirements.
TEACH requires that the academic institution meet specific requirements for copyright compliance. For the full list of requirements, refer to the United States Code, Title 17, Section 110.
It is also important to note that TEACH does not supersede fair use or existing digital license agreements.