when does it no longer become the owner's property?
Now, in the US, 70 years after the death of author. If a work of corporate authorship, 95 years from publication or 120 years from creation, whichever expires first.
Copyright term has gotten entirely out of control. The issue is that the value of most works is pretty much nil shortly after publication. But there are a few works that remain valuable for a long time.
Corporate interests hi-jacked Congress and locked up a lot of primarily worthless stuff that people could nonetheless make good use of, for the sake of preserving copyrights in the extremely small quantity of stuff with lasting value.
Remember Walt Disney's "Song of the South" with Uncle Remus, B'rer Rabbit et al.? Would you like to see it again? You can't. Because of the dated racial overtones in that work, Disney keeps it locked up, so it is not even available for, say, study as a social science time capsule.
Consquently, there is a lot of material out there which (a) you can't use, and (b) you can't even find the owner to find out if they care. This is the "orphan works" problem.
Orphan works is preventing the generation of derivative works, or use within other works, and essentially undermining one of the aims of copyright, which is to encourage the production of creative works. Just as Disney made a fortune recycling old folk tales into animated cartoons, creative works build on each other. Copyright was intended to encourage production of creative works by ensuring a right to profit from their production, but it is now strangling the well of artistic and cultural resources.
A proposed solution was to establish a set of diligence standards for someone seeking to use a presumptively copyright work, and if you can't find the owner, then to have a standard mechanism, through the Copyright Office, of providing information about your search and your use, along with a fixed royalty that you would pay if the owner pops out of the woodwork along the way.
A lot of organizations, including those representing photographers and other author interests, became concerned that an orphan works licensing mechanism would provide a short cut to ripping off material that was still economically valuable to the author.
The present situation is a frustrating stalemate.