The Mona Lisa with a Mustache

Derivative works also stir up plenty of migraines among the geekerati. These are creations that include major, copyright-protected elements from another work.

Read here about a case lost by the artist Jeff Koons, who told artisans to transform a greeting card into four sculptures, which sold for $367,000. Unfortunately, he didn't gain permission from Photographer Art Rogers, who'd snapped the couple holding eight puppies.

So what does this mean for bloggers? Mainly be careful when compositing together illustrations – and vigilant when your material is thus remixed. Fair use allows you to write a Buffy the Vampire Slayer spoof and publish a collage of images ripped from newspapers, if you can find any these days ... The exemption also permits Google to run thumbnails of your images in its search engine, thanks to the Perfect 10 ruling. Judges deemed this "transformative because it provides an added benefit to the public, which was not previously available and might remain unavailable without the derivative or secondary use."

The most famous example of this is Marcel Duchamp's parody of the Mona Lisa. He added facial hair and the caption L.H.O.O.Q, also the work's title (it translates as "she has a hot tail"). He transformed a cult icon into an object of ridicule to critique the bourgeoisie.

For a something to be derivative and kosher, it must display originality of its own, containing sufficient new expression over and above the earlier work's. As Judge Pierre N. Leval noted in a landmark Harvard Law Review article: "Transformative uses may include criticizing the quoted work, exposing the character of the original author, proving a fact, or summarizing an idea argued in the original in order to defend or rebut it. They also may include parody, symbolism, aesthetic declarations, and innumerable other uses."

We'll talk more about piracy, copyright and protection week ten.