A little late to the party, I thought I'd try the old "transparent screen" trick. The process is fairly simple:
- take a picture of your computer screen and its surroundings.
- take an identical picture, but this time remove your computer screen first (and then put it back exactly where it was).
- using the first picture as a guide, select the part of the second picture that corresponds to the actual display surface of your screen.
- reshape it to a rectangle of the same size as the full screen resolution, save the image and make it your desktop background.
- take another picture from the same spot as before, and voila! your screen looks transparent.
(You could skip the first picture and just wing it, but it's a lot trickier.)
You can see the result of my half-assed first attempt above. It's basically a five-minute test gig done using the camera in my phone in crappy lighting, but you get the idea...
I couldn't help thinking, though, that it shouldn't be all that difficult to automate most of the process. As long as the first two pictures are taken from exactly the same position (using a tripod wouldn't hurt), the crux is to find the screen within the first one. I don't know exactly how to do it, but I suspect it's a relatively simple form of image analysis. Displaying some extreme color (think blue screen/chroma key) full-screen while making the first shot should help.
I just may have to give it a shot.