A Micro-Puzzle on French Banknotes
Microprinting has been used as an anti-counterfeiting technique on banknotes for many years. Text is printed in a size that is unreadable to the naked eye, but easily visible under light magnification or digital scan at 600dpi. Hand engraving the fine details of any banknote may be tricky, but accurately reproducing microprinted text is virtually impossible. It is easy to recognize a poor print quality, misaligned text, or the fuzzy reproductions made by scanners and printers.
Most microprinted text is relatively mundane, consisting of repetitive sequences of the country name, or the note's denomination, or sometimes the text "BdF" (for Banque de France) simply used to accomplish the literal need for some text that can be verified later to ensure the authenticity of the note.
In 1993, France issued a truly modern set of banknotes, featuring Antoine de Saint-Exupéry, Paul Cézanne, Gustave Eiffel, and Marie and Pierre Curie, which has the typical suite of security features that we see in modern banknotes today. Among others, these features include color-changing inks, "invisible" inks, security threads, and of course microprinting. The microprinting at the upper left of the notes and the lines extending into the watermark area of the 100F and 200F notes, took an interesting turn from the traditional. Hover your mouse over the images below to zoom in to find the microprinting on each banknote.
Below is a close-up crop of the 50F Saint-Exupéry note, showing a section of the microprint in the upper left corner. Aside from long strings of jumbled characters, it's hard to distinguish much from this text. Spending some time with Google wasn't helpful, and more surprisingly, neither were the specialized French catalogs. Was this some sort of Da Vinci Code I'd found?
If you want to figure this puzzle out yourself, don't read any further. Grab a piece of paper and a pencil, and go at it!