Creating a secure identification for the many products being sold remains a challenge. You want to have a secure identity, impossibile to duplicate, and you also want to have it cheap so that it can really be used.
There is basically nothing that cannot be reproduced, but the point is the cost of reproduction. If it would cost much more to duplicate an identity than the value of the product itself there wouldn't be any incentive in doing that.
This is the result achieved by a group of researchers in South Korea.
They have found a way to scatter some twenty silver nano rods coated by a fluorescent dyes and freeze their position by embedding them in a plastic sheet. This creates a unique pattern that is practically impossibile to reproduce.
Each nanowire has a diameter of about 70nm and a length between 10 and 50 µm. They scatter in a random way that is impossibile to duplicate (at least within reasonable cost - IBM has shown several years ago a way to push a single atom into a specific position but that is a feat requiring an extremely complex apparatus and a long time....).
The fluorescent dyes make the pattern visible optically, through an optical microscope but potentially also through a smart phone camera, and this pattern can be compared with the original one to ensure that it is not counterfeited.
Interestingly the authentication process can be automated in such a way that any given pattern is given a unique identity (a number) so that one does not need to store the image and compare the image but just a number and compare it with the number calculated by the analyses of the pattern detected by the terminal once observing the image.