According to the Library of Congress, "copyright refers to the author's (creators of all sorts such as writers, photographers, artists, film producers, composers, and programmers) exclusive right to reproduce, prepare derivative works, distribute copies, and publicly perform and display their works."
Understand Fair Use
"Fair Use" is a provision in US copyright law that imposes limits and exceptions to the exclusive rights of copyright owners.
It means that you can use copyright-protected media without asking for permission if it is considered for a fair purpose, such as criticism, comment, news reporting, teaching, scholarship, and research.
If you use any icons or images that you did not make, make sure to cite their source. Preferably, you should find icons or images with a Creative Commons-license.
To cite an icon (all licensed under Creative Commons) from The Noun Project, follow their attribution guidelines:
To cite an image or icon that does not include explcit attribution instructions, include at least the name of the creator, the licensing information, the title of the work, and a link back to where you found it.
For example, above is a screenshot of the author and copyright information for a photo titled "Notebook Collection" found on Flickr. To cite this photo, you might use a format like this one:
Almost everything is copyrighted and requires permission from its creator to use. There are, however, some exceptions:
"Specially-licensed" - There is a lot of media that has been made available for anyone to use, waiving the need to obtain direct permission from the author. For example, a very common license is an "Attribution" license, meaning that you can use the media for any purpose as long as you give credit to the creator somewhere in your work. The non-profit organization Creative Commons offers a variety of attribution licenses that creators apply to their work to make available for public use. Learn more about Creative Commons licensing. Search for works with a Creative Commons license.