It gets even more mucky under the DMCA. I no longer have to register my copyright with the copyright office (part of the Library of Congress) to have a valid copyright.
Let's take a real world example -- say I bought a bunch of Steve Jordan's books. (I have and they are great, check them out.) What do I have?
I have an electronic copy of the book and a good copy of a color cover. So what can I do with that?
I could post the files on my web site and sell them. As long as Steve doesn't catch me he loses pay for every copy that is downloaded.
I could post them on the darknet and perhaps kill all of his sales for while.
Are any of these actions legal? No. I have no rights to distribute his works. If he fails to enforce his rights he is subject to having those rights stripped from him. If I posted the works (even for free) and he becomes aware of it and fails to exercise his rights the works may fall into the public domain. It is a civil matter which means that the Government will not take any action on its own, but only as Steve goes to court to get them to exercise a judgment against his works being posted elsewhere.
Was it illegal to post Steve's works before he noticed and told me to take them down? Yes. Then there is the secondary point of damages. How much does Steve want? This is why lawyers get the high fees that they charge.