Overture (which may not be made any more under that name) can read scanned sheet music and play it or turn it into editable sheet music or a MIDI.

Here's a link to Coda Music's "Finale: Guitar," which sells for $99.
Finale Guitar

Click where it says "Enter Notes," and you will see that there are several ways to enter the notes, including SCANNING sheet music and playing a SINGLE NOTE instrument.
If your voice doesn't have a lot of distracting overtones, I'd imagine you can plug in a miked voice instead of a piano or guitar.