Where the line is drawn can be subjective and can be used to punish what started out as good intentions just as much as it tries to protect the original work. Let's set that aside for a moment and talk about the concept of open source.
It's different than crowd sourcing, and different than copying. You hear the tern a lot from the IT industry, and in journalism -- have you noticed lately how many times pictures and quotes are pulled from Facebook and Twitter? I can't possibly do any better explaining it than the excellent TED Radio Hour pod cast I just listened to. You can download it via iTunes or your favorite pod cast listening app (mine is Stitcher), or straight from their web site here. It starts with discussions in the internet and the origins of Linux, but then talks about open source house design and ocean exploration.
I am endeared to Corina Tettinger forever because she specifically stated in the class I was in that using her techniques to make similar beads was totally ok with her. It got me to thinking that perhaps all creative folks, especially those that teach, should adopt this open source mode. Think of all the beautiful things that can be made with collaboration!