Copyright has often been thought of as a very complicated thing that nobody can understand. At the root of it, however, the rules of copyright are very simple. What makes it complicated is all the exceptions to it that have been added by certain groups of people. These exceptions allow them to do specific things to copyrighted works under specific terms. One would have to ask a question as specific as the exceptions themselves in order to get a "straight answer" out of the copyright law, and very few of us would care to do so.
The copyright law became even more complex when computers and the Internet came along. Today, making a copy of something is literally a mouse click away, and even unavoidable as the computer makes several copies inside its RAM and on the hard disk when executing programs and editing documents. Worldwide distribution of a work is as easy as dropping a file into the window of an FTP client.
Something as big and complex as copyright law is better understood if one starts with the basic rule behind it and builds upon that, in the same fashion as the whole thing was built in the first place. So here we go.
The basic rule behind copyright is that the creator is given certain rights, including distrubution of the work, but can't control what happens after a copy is sold; the user can do whatever they want with their copy, as long as they don't do anything that discourages the creator from creating more works (such as distributing copies themselves).
Once you understand that, you're ready to build on it.
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