EDIT: I just realized this doesn't say anything about what the block is. It takes an object input, gets said object's costume, compiles from pixels to the form of sound samples, then plays the sound. This doesn't have any practical use (unless you want random sounds playing) without a reporter, and just plays the sound it makes immediately after creating it. Yeah.
Anyway. This was something I'd been dabbling in for a little bit, but I figured it out now and I think it's pretty cool!! I also included some code (outside of the custom block) that shows how a bit of the source code of the block works and takes a photo through the webcam and turns that into a sound. Overall, I think this is pretty cool. Visual music, everybody!!!