Hi,

As an interim step to total electronicization of money I believe that
2D barcodes on banknotes should uniquely sign the note, so any imaging
network device could tell if the bit of paper was a duplicate, and help
tracking. A non-networked device should be able to check the
signature, but not do real-time tracking. If your money was stolen you
should be able to receive your stolen property when it was handed into
a bank. (Or is ownership of banknotes lost upon theft? - uk.legal)

2D barcode technology is well developed and used for example in
franking machines. There may be reasons why not to introduce the
technology such as to let dollar bills be the currency of corruption.

Dave.