Any type of media, (books, magazines, newspapers, videos, music, photography, art, etc.) can potentially be in the Public Domain if it meets one of four common copyright conditions:
> The copyright has expired
> The copyright owner failed to follow copyright renewal rules
> The copyright owner deliberately places it in the public domain, known as “dedication”
> Copyright law does not protect this type of work.
Now you might think, “Why would anyone NOT renew their copyright?” It's a great question with many answers, but it ultimately doesn't matter. What DOES matter is that the media IS INDEED in the Public Domain...and that can be determined in a straightforward manner MOST of the time. I'm not going to bore you with all those details now, however, because there is a much different picture I want to paint...
Check THIS out: Worldwide, there are over 2 billion books in the Public Domain, millions of magazine articles, 100's of millions of art, photography and illustrations, millions of patents, not to mention all the video and audio content, web content and more. The Public Domain is SO huge that it's virtually inexhaustible!