There is provided a framework to record to a blockchain unique identification (signatures) of physical items which have unique, random properties. Physical items are analysed using spectral imaging to determine the unique identifications. Hardware is shown to perform the analysis and various nodes of a peer-to-peer network are shown and described, which nodes may be configured to provide proof of location, privacy, trust and authentication. The solution can work even if the item is modified in some way if a subset of the unique properties remain.