If a piece of art or other work is old enough, it becomes public domain, like Da Vinci's "Mona Lisa." That means anyone can reproduce it at no charge—the original creator (who is long dead) no longer holds copyright to it. Nobody owns it anymore, and it is free for anybody to use as they wish, including doing funny things with it.
In Canada, the works of an author generally become public domain 50 years after the end of the year in which he or she dies (sooner, apparently, for music recordings—does that mean early Elvis recordings are free for the taking here now?). So, for instance, the paintings of Emily Carr, who died in 1945, became public domain over a decade ago.
Interestingly, Michael Geist points out that many musems and galleries attempt to assert copyright over reproductions of public domain works, including Emily Carr paintings, and charge significant fees to make those reproductions.
But, he argues, court cases are beginning to establish that "while museums are understandably searching for revenue streams, doing so on the basis of misleading copyright claims is not the way to do it." We all need to remember copyright law, like patent and trademark law, is not like a law of physics; rather it is a human invention designed to foster creativity by balancing the rights of creators and the general public.