So well said. Some valid analogies made.
However, did you know that the rights to many old paintings are owned by someart museums? That is something I have learned through shooting for stock, an my son working in an art museum. Those "free" paintings are not fair game.
Photo licenses really expire only when agencies and photographers terminate a contract. Licenses don't just simply expire. I think you may be thinking about the copyright issue of photographs - they are still copyrighted until 70 years after the photographer's death. Copyright Duration can be checked by clicking on the link.
Also, when someone licenses an image, especially a Rights Managed image, the person licensing it is restricted to a time frame of usage.