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UK flooded with forged stamps despite using barcodes — to prevent just that
(www.bleepingcomputer.com)
This is a most excellent place for technology news and articles.
I believe counterfeit stamps is always a problem but never been discussed publicly, though I can't deny the barcode could be used for other purposes like tracking internally.
And you're right at counterfeiting 1 dollar bills analogy. People can just print and mail it at a lower than what real stamp cost, sell it to unsuspicious people and earn the difference.