A copyright owner has the exclusive right to copy, publicly perform and distribute the copyrighted material and to prepare derivative works. Copyrights can be transferred, and any or all of these rights can be licensed. Not all copying is prohibited. This permits copying for purpose of scholarly research, commentary and similar activities. The courts apply a multifactor test that looks at the purpose of the copying, the amount of material copied and the impact of the copying on the market for the copyrighted work.
Fair use is a somewhat limited defense.
Registration of copyright. Registering the copyright with the Library of Congress is not required to have a copyright. However, with certain exceptions, you must register the copyright before you can bring a lawsuit for copyright infringement. In the case of computer software there are special rules that allow you to file only a portion of the computer code. Prior to 1989, it was necessary to put a copyright notice on a work in order to obtain a copyright in a published work.