Advances in photocopying technology allow criminals with no printing expertise to counterfeit paper currency  One standard anticounterfeiting technique, microprinting, prints paper currency with tiny designs that cannot be photocopied distinctly  Although counterfeits of microprinted currency can be detected easily by experts, such counterfeits often circulate widely before being detected  An alternative, though more costly, printing technique would print currency with a special ink  Currency printed with the ink would change color depending on how ordinary light strikes it, whereas photocopied counterfeits of such currency would not
Because this technique would allow anyone to detect photocopied counterfeit currency easily, it should be adopted instead of microprinting, despite the expense
When an anticounterfeiting technique depends on the detection of counterfeits by experts, the cost of inspection by experts adds significantly to the cost to society of that technique.