A public domain work is a creative work that is not protected by copyright and which may be freely used and adapted by anyone. The reasons a work is in the public domain may include:
Creative Commons is a nonprofit organization that enables the sharing and use of creativity and knowledge through creative commons licenses. These licenses allow creators greater control over their ability to share their work and allow others to use it. Creative Commons is a great resource for finding materials to utilize as well as sharing your work with the world. The website contains a section dedicated to Public Domain Tools.