True -- virtually everything contained in books you'll find at these locations were protected by copyright. But ... it's also true that many of these copyrights have expired -- making contents of those volumes completely public domain.

US copyright law has gone through several iterations -- but two things you need to remember are "75 years from copyright date" and "Sonny Bono"!

The copyright law originally stated that a copyright would last for 75 years. Thus, if a book were copyrighted in 1900, copyright would expire in 1975. If a book were published in 1920, copyright would expire in 1995. If a book were copyrighted in 1922, copyright would expire in 1997. But ... if a book was copyrighted in 1923 or later, then things take on a whole new slant ... courtesy of then-Congressman Sonny Bono.

You see, a particular item was originally copyrighted in 1923. It's copyright was due to expire in 1998 -- sending this item into public domain. This is normally not a problem -- truthfully, most people don't care about things copyrighted so far back. Expiring copyright can actually grant these works new life in public domain.

In this case, though, item due to expire was a mouse -- Micky Mouse!