In the key of C minor

Bonus points for anyone who can identify today's photo source...

Today, Billy invited me...yes, ME!...to join him in a duet. Billy is an amazing piano player. I can manage to find middle C and that's about it. But he explained we were going to play in C minor, showed me the notes in that key, and said I could play any of those notes, any way I wanted. And away we went...and it sounded good...

The photo is the "belly" of the piano, inside the lid.