Stephen Lewis's Processing file test.pde tracks multiple blobs and turning them into a tone melody. Clicking the mouse on any pixel re-assigns that pixel's color to be the tracking color, but it starts on black, so it can follow shadows on the backlit table top. The table is actually a piece of mylar inside a plexiglass holder suspended above a camera in a garbage can. All materials available at Staples, including the garbage can, mylar (or tissue paper) and plexi. You can also buy a webcam at Staples.

His program uses the ESS library which makes audible tones. ESS is at, but also listed on the processing help file under "libraries". The JMyron vision library is at, but also listed directly in Processing's reference help file. Expect it to run at about 5 frames per second.

There's also a brightness tracking library right in Processing's examples menu, which uses a brute force pixel-examiner algorithm to find the brightest pixel (no centroid or extents or anything about the bright-pixel being in a blob, so it's a bit random and jittery). Expect that to run at around 30 frames per second.