Copyright protects original works that are fixed in a tangible form. Fair use allows limited use of copyrighted works for commentary, criticism, parody, and education without permission. To determine if a use is fair, courts consider the purpose of the use, nature of the work, amount used, and economic impact. Works in the public domain are not protected by copyright and can be freely used, including works where the copyright has expired or the author is unknown. Creative Commons licenses provide alternatives to traditional copyright. Registering a copyright makes it a public record and allows for statutory damages. Licensing allows copyright holders to sell limited rights to use their works for a fee.