In researching a little side project, I came upon a cool site that collects old-time piano rolls and uses software to scan them and convert them to MIDI. It's a very cool project since before recording equipment was invented, a player piano that used rolls was the only automated way (as far as I know) to play back a song. It makes sense to use MIDI since piano rolls were the precursor to MIDI. To quote Wikipedia, "Piano rolls have been in continuous mass production since around 1897. Though they are still being made today, MIDI files represent a modern way in which musical performance data can be stored. MIDI files accomplish digitally and electronically what piano rolls do mechanically. Software for editing a performance stored as MIDI data often has a feature to show the music in a piano roll representation." PianoDisc is a cool technology that combines the two.