"Definition of public domain: The public domain is generally defined as consisting of works that are eitherineligible for copyright protection or with expired copyrights. Public domain refers to the total absence of copyright protection for work The public domain is a range of abstract materials commonly referred to as intellectual property which are not owned or controlled by anyone. The term indicates that these materials are therefore "public property", and available for anyone to use for any purpose."
"No permission whatsoever is needed to copy or use public domain works. Public domain material is available for anyone to use for any purpose, private and commercial. Public domain works can serve as the foundation for new creative works. Public domain works can also be copied and distributed without any permission or paying royalties."
"Public domain works ("works in the public domain") are considered to be a part of the "public's cultural heritage, anybody is entitled to make use of them for any purpose, including copying, modifying and even selling. Moreover, it is even permissible to remove the original author's name. The public domain can be defined in contrast to several forms of intellectual property; the public domain in contrast to copyrighted works is different from the public domain in contrast to trademarks or patented works. A creative work is said to be in the public domain if there are no laws which restrict its use by the public at large. Public domain is a phrase that describes something that belongs to all people in general. It is "public property"."
How and when works become part of the public domain? More on Public Domain Definition
Resources of public domain materials:
- Public Domain Images Several thousand copyright friendly digital pictures nicely organized in folders, free for any personal and/or commercial use, credit or back link is not required.