Copyrights attach at the time of creation. This means that whenever anyone writes something, paints something, etc., it is entitled to copyright protection with no formal filing process required. Anyone may use the symbol (©) freely in order to announce their reservation of rights in the material. However, copyright notice is optional, so your work is automatically protected whether you place a notice on it or not. One caveat, copyright registration is required before the copyright owner can sue in federal court for an act of infringement. Further, the rights and damages that a plaintiff may recover are greater if the copyright is federally registered before the infringement is commenced.
To determine whether use of a copyrighted material is fair-use (meaning that your use does not infringe the rights of the copyright holder), 4 factors are used:
Purpose and character of the use (is it transformative?)
Nature of the copyrighted work
Amount used (quality and quantity)
Effect on the potential market
Currently, for a regular person, a copyright claim will last the lifetime of the author plus 70 years. If the work is owned by a legal entity, such as a corporation, the copyright receives a flat 95 years.