Intellectual Property Law
Intellectual property law questions? Ask a lawyer
Copyright infringement occurs when copyright protected material (original and creative work) is copied either exactly or with substantial similarity. Copyright does not protect concepts or ideas, but rather, only the expressive elements of a work. So it depends on if you are copying the expressive/creative elements of the work. also, the amount you "copy" matters to, relative to the work itself as well as your work.
for more info on copyright protection & infringement, see http://coursecracker.com/4/7487/College/Law/Intellectual-Property-Law/links/index.html
A derivative work is an expressive creation that includes major, copyright-protected elements of an original, previously created first work....but whether it is a "derivative work" or just an infringing work doesn't really matter from your standpoint because you don't want to do either, they are both infringement. But you can't have a derivative work without substantial similarity or some key elements being copied.
the spectrum is a way to think about infringing acts but the main test is whether you have copied/borrowed the expressive elements of the work and to what extent, so you should use your best judgment on that e.g. are you putting it in your own words or essentially plagiarizing?