Volker Hetzer wrote:


Actually, today banknotes aren't naively stuffed fithe anti-forgery-features
but the idea is to make it unprofitable to fake a banknote in a small-scale
production. So, a forger is forced to go large-scale which in turn is easily
detectable (duplicate serial numbers or unexplainable inflation for instance)
and which also justifies a large-scale counteraction to find and disable him.

I am not sure duplicated serial numbers or unexplainable
inflation, especially the latter, are practical
characteristics that are 'effectively' checkable.
(Define 'unexplainable inflation'!) It's 'olds' now that
e.g. 50 Euro banknotes had been forged quite well. They
were presumably produced in regions not within EU
influences. Someone told me that certain sophisticated
techniques previously employed in DM are not used in Euro
because Euro is made by diverse member countries and not
all of them had such techniques at their disposal and so
they agreed on sort of a gcd.

M. K. Shen