My flatbed-scanner-based piano roll scanner suffered from a deficiency
in that it couldn't reliably decode the various rewind punches which
the various manufacturers employed.  This is just a note to describe
my solution:

I made a bunch of 0.75" x 0.75" stickers with a QR code printed on it
(embodying the string, "End Of Roll"), and stuck one somewhere near the
end of the roll.  My scanning software then searched for the QR code
at each incremental iteration, halting the scanning operation upon its
discovery.  Ten rolls so far suggest it works quite well.

Marshall Jose