Any suggestions on a possible methods that people can verify
authenticity of a product? Something not as expensive as smart cards
that can be placed on the packaging like a tin of milk or box of
cereal? that the user can probably pick up his phone and verify it's
If you're going to make it that easy to authenticate, you're leaving yourself wide open to fraud. I also think you're overthinking the problem.
Let's say I'm making action figures. I would imprint in a few places unique "flaws"-- perhaps on the bottom of its foot, a tiny groove here, in its hair, one of its locks may be arranged in a very particular curl. Then I would also imprint a batch number anywhere on the item-- maybe "16" for being the current year's model, but hopefully something less obvious.
You introduce all of these quirks and document them for yourself. "On series #16, I should expect to find x on its foot, y in its hair, etc."
Then for the next batch, you change up these flaws. And document it again.
The trick here is that you DO NOT publish the list of flaws. Any counterfeiter that comes along is ideally going to not notice them at all or assume the flaws resulted from the manufacturing process and will not bother to replicate them. Or even better, the flaws are so fine that their machinery can't replicate them.
If you do publish the list, then the counterfeiter knows exactly what flaws to replicate.
So in the end, YOU need to be the authenticator, not some phone app. If someone has any questions about authenticity, you have them send you high-resolution pictures of their item, its series number and YOU look for the verification flaws that would prove the item legit-- without telling them what exactly you're looking for.
If you care, set up some kind of legal arrangement where upon your demise, that list does get passed on to some trusted third-party so your works can continue to be authenticated in the future.
You could probably charge some money to perform this service if you were so inclined.