“The Possibility of Making $138,000 from Shredded Banknote Pieces Using Computer Vision”, 2023-11-17 ():
Every country must dispose of old banknotes. At the Hong Kong Monetary Authority visitor center, visitors can buy a paperweight souvenir full of shredded banknotes. Even though the shredded banknotes are small, by using computer vision, it is possible to reconstruct the whole banknote like a jigsaw puzzle. Each paperweight souvenir costs $100 HKD [ie. ~$10 USD; “trading since May 2005 in the range US$1 : HK$7.75–7.85”], and it is claimed to contain shredded banknotes equivalent to 138 complete ($1,000) HKD banknotes. In theory, $138,000 HKD can be recovered by using computer vision. This paper discusses the technique of collecting shredded banknote pieces and applying a computer vision program.
…The shredded banknote pieces were enclosed in a cylinder of proxy glass in a cylindrical container. Proxy glass melts at ~200℃; a household hair dryer would be sufficient to soften this glass. Figure 3 shows the lid being removed using a heat gun.
The shredded banknotes were then collected. Surprisingly, 3 paperweight cylinders were opened, and two of them had stones in them (Figures 4 & 5)!
…Because one of the 3 cylinders contained some stones, the fourth cylinder was opened with care. The weight was recorded for each step. The label on the cylinder claimed that it contained 138 pieces of equivalent shredded banknotes. By comparing the weight of the shredded banknotes with that of the actual banknote, the number of equivalent shredded banknotes could be calculated…It was surprising that the Hong Kong Monetary Authority had provided only 20 equivalent banknotes rather than 138 equivalent banknotes. The cylinder only contained 20/138 (= 14.5%) of the shredded banknote pieces that the label had claimed…This cylinder only contained 82.57/138 = 60% of the shredded banknote pieces that the label had claimed. Although this issue is not the focus of this paper, it appears that the Hong Kong Monetary Authority has broken the law.
…The idea for this paper was discussed with the staff during my visit to the Hong Kong Monetary Authority visitor center. The paperweight souvenir is currently no longer available.