Why can’t you scan, photocopy or print banknotes at home?

It is literally impossible to use an inkjet printer or photocopier to scan, photocopy or print banknotes because of a security measure that prevents it. It is a geometric pattern composed of five circles of barely one millimeter in diameter each, which appears repeatedly “camouflaged” as part of the design of banknotes. Although it is not used in all the world’s currencies, it does appear in the euro, the US dollar, the Mexican peso, the pound sterling and the Swiss franc, among many others. It is estimated that it was first implemented in approximately 1996, although its purpose was only discovered in 2002, and since then it has been unofficially known as the EURion Constellation.

Something really striking is that its development and implementation has taken place under absolute secrecy. This feature has not been given an official name and central banks do not talk about it either. Therefore, specific data on how it works are still unknown; moreover, it is presumed that it was developed by a Japanese company, but this has not been confirmed so far. The peculiar thing is that its purpose was discovered by chance in 2002 when computer scientist Markus Kuhn tried to copy a £20 bill with a new color photocopier, but was unsuccessful. The machine handed him a sheet with a message printed in different languages explaining that counterfeiting money was illegal.

Intrigued by the situation, Kuhn noticed that the paper money he had tried to copy included recurring circles “disguised” as musical notes. Simultaneously, he picked up a 10-euro bill – which had entered circulation that year – and saw that it featured rings in the same pattern. Clearly, it was no coincidence.

Through further research, he coined the term EURion Constellation to refer to this mysterious security measure, taking into consideration the similarity of its design to Orion. And as he probed deeper, Kuhn noticed that the copying machines not only identified the presence of the geometric pattern, but also its color.

What happens if I try to photocopy banknotes?

Before we go any further, a logical but necessary caveat: counterfeiting money is a crime all over the world. Therefore, trying to print money at home – be it through the scanner of a multifunction printer, with a photocopier or any other available method – is illegal. It doesn’t matter if it’s just out of curiosity and for no malicious purposes; just don’t do it.

That said, there are countless videos on YouTube that clearly show what happens when it comes to photocopying banknotes: it doesn’t work. Any modern banknote with the EURion Constellation simply cannot be replicated in this way. The end result of the printing varies depending on the equipment used, but in all cases the copied image ends up ruined. In some cases, the banknote is copied in its entirety, but with white stripes that cut into the print and colors that are more “washed out” than those of the original paper money. In others, the equipment prints the banknote halfway through and then “spits out” the sheet, while in some cases it does not print at all and releases the blank sheets.

It is evident that the geometric pattern incorporated by central banks is effective in preventing anyone from printing their own money. It is true that banknotes can be photocopied completely in black and white – which supports Markus Kuhn’s theory that the EURion Constellation depends not only on the detection of the circles, but also on their color – but they are clearly useless.

You can’t edit banknotes in Photoshop either

Another interesting point is that some of the most recognized programs for image editing do not allow you to edit photographs of banknotes. In fact, it is not even possible to open them. The most notorious case is Photoshop, without a doubt, but it is not the only one.

And if you wonder how a software can automatically identify that you are trying to work on an image that represents some kind of fiat money, you don’t have to think too hard to find the answer. Just like a scanner or a photocopier, they include a counterfeit deterrent system (CDS), although in this case the EURion Constellation has nothing to do with it.

Professor Steven J. Murdoch published a very interesting paper on this subject in 2004; and even then he concluded that detection via software probably relied on some hidden watermark, undetectable to the human eye, rather than the geometric pattern. Once the attempt is detected, it will insert forensic tracking data (e.g., steganographically encoded binary data) into the resulting copy and can communicate with a remote service and report the attempted reproduction of a banknote.

Combating counterfeiters

It is true that counterfeiters’ methods have also become more complex and elaborate over the years. But laying strict foundations to prevent any individual from making illegal copies of a banknote with just a scanner or printer has its logic. Or at least it did when these devices started to become more accessible to the general public.

At the same time, this also makes it clear that we still do not know much about how much work is being done to prevent counterfeiting of money, especially the world’s most important currencies, such as the U.S. dollar and the euro. And beyond geometric patterns, algorithms and watermarks, it wouldn’t be surprising if there were already other methods of protection that we can’t even imagine.

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