decryptionJul 1
one of these sheets of stamps is counterfeit, the other is genuine - I honestly can't tell from these scans which one is which (I scanned them in a few hours ago and even I forgot which one is which) full res versions: https://images.heyinternet.com/stamps.zip
Show threadJames HenstridgeJul 1

@decryption At some point, they'll probably have to put a unique serial number + digital signature on each stamp. Counterfeiters might be able to copy the serial number, but it'd be possible to see if a number has already been used for postage.

That'd still leave the problem of regular people not being able to tell the difference though, so isn't a complete solution.

Show threaddecryptionJul 1
@jamesh i think they already do this with the Priority labels (70c each that you stick next to the regular stamp) - so not sure why they haven't moved the normal stamps to the same system. They're losing tens of millions of dollars, if not more, every year.
Show threadJames HenstridgeJul 1

@decryption It looks like the UK has done so with a barcode section on the stamps now:

https://www.royalmail.com/sending/barcoded-stamps

I'm still not sure how a regular person could tell whether a particular barcode has already been used as postage.

Show threaddecryptionJul 1
@jamesh you’d think scanning it with an app on a phone would be common sense, alas
Show threadJames Henstridge

@decryption There's still lots of room for screwing people over.

If you bought a roll of 50 stamps, would you unroll it and check every stamp for authenticity? Or would you check the first few and assume the rest were okay?

If a counterfeiter put 5-10 valid barcodes at the beginning of a roll and dummy ones after, would you notice? Or if they took a full set of barcodes and printed them in reverse order on a second set of stamps: they'd almost all appear valid at first, but you'd run into problems ~ half way through.

Jul 1 at 4:36amWeb
Show threaddecryptionJul 1
@jamesh i wonder if there are any fake UK stamps with the QR codes
Show threadJames HenstridgeJul 1

@decryption Maybe?

I guess it might be good enough if there is doubt about whether counterfeit stamps will be accepted.

There'd also be a limit to how complicated it is worth making the security features. Unlike a bank note that will be reused hundreds or thousands of times, a stamp is used once.

Show threaddecryptionJul 1
@jamesh oh there's a cottage industry of people re-using stamps (in Australia at least) since aus post has stopped marking them as used!