Copyright is a topic that hits close to home for me, as I teach a course called Concert Media Design, and visuals for productions are the main focus of this course. While much of what I focus on is the technical aspects of the gear, such as media servers, display devices, etc, a designer must also be focused on creating content for concert productions. One of the topics that I stress to my students is that "right clicking and save as" does NOT make the content yours, even though it's now on you computer. For years, copyright on visuals is something that was not a big issue in concerts, as most of the visual look was provided by the lighting. (Although, there are some cases where lighting designs and set designs for broadway productions have been copyrighted, and court cases have arisen when those productions went to off-Broadway tours, and the designs were basically re-used by other production companies)
With the advent of media servers, devices that allow real time rendering of visual content to be displayed on stage, copyright has become a large issue. There are cases of visual designers being sued because they have used somebody elses visuals without proper permission. To me, this is very much like the Girl Talk situation, although it focuses on visuals instead of music sampling. My goal in teaching about visuals in my course is to stress that my students need to create their own visuals in order to be absolutely sure that they are not infringing on protected works. Yet even in the process of creating their own visuals, it is possible that they could still be in violation. One example that I use is if a student takes a digital picture with their camera, they can use it as their own content. But, if the picture is of the McDonald's golden arches, then they could still be in violation of the law, and can not use that in any way they deem fit.
In January, I conducted an interview with Bob Bonniol, a creative designer and media producer for live performances. Bob's company, Mode Studios, creates content and supplies technical work for everything from ballet to rock and roll concerts to architectural installations. I feel that his take on copyright is very good, yet even he has some "grey area" in his own interpretation.