Wow, I was pleasantly surprised by the positive feedback I got on my copyright spiel.
It is true that proving copyright infringement can be tricky. Just for the heck of it, here is my attempt to outline the elements of copyright infringement...
DISCLAIMER: this is not legal advice. I am not a copyright lawyer, I am just a dork who took some Intellectual Property classes in law school; do not assume that I necessarily know what I'm talking about (always a good rule of thumb, really).
- It must be proven defendant was familiar with the copyrighted work. Obviously, you can't copy something if you've never seen/heard it before, and there's no infringement unless there was copying. In an oft quoted decision, Learned Hand asserts that if someone who had never read the poem Ode to A Grecian Urn (assuming it is protected by copyright, which it isn't) by some coincidence managed to pen the same exact poem, not only would he not violate Keat's copyright, but he would he would hold a copyright for his "original" work. This element of an infringement claim is usually met by offering circumstantial evidence that the defendant likely came across the original work.
- Defendant must have copied plaintiff's protected work. This element is usually met by proving that the allegedly infringing work is substantially similar to the protected work.
- The copying must amount to infringement. (and I'm saying this is an element of copyright infringement? If that isn't begging the question I don't know what is. Anyway...) Did the defendant merely copy "ideas" which are not protected or did he copy "creative expression"? Are the copied elements generic (like the stereotypical drunken Irishman in Nichols or the caped superhero) and thus part of the public domain? Even if the copied elements are indeed deemed to be non-generic, creative expression there is still a threshold test: if someone copies (without the original author's permission) a line from a song, a shot used in a movie, a particularly apt turn of phrase in a book, perhaps even a character, this borrowing/stealing a small element of creative expression from a protected work may be considered "fair use" and thus would not constitute copyright infringement.
One more basic point about copyright law: remember that copyrights only last for a limited time. Under current US law, the term of a copyright for a work created today is the Life of the Author + 70 years (or simply 120 years if the author is a corporation or some other kind of non-natural person). US copyright law used to be more complicated than this, however, and some older works are governed by the rule in effect at the time they were created. Also good to know: the copyright for all works created before 1923 has expired and all these works have fallen into the public domain meaning people are free to use them as they wish.
Have a good weekend everybody!