How to discuss the complex notion of originality
Here's an NYT lesson plan with lots of resources to address the issue of plagiarism among high school students. (Some of the links might be useful for upper intermediate as well.)
"Do your students have a hard time defining — and thus, perhaps, avoiding — plagiarism? They're not alone. In a cut-and-paste world, examples of both intentional and unintentional plagiarism are everywhere."