[I was unsure whether to post this in Money.SE, GraphicDesign.SE, or Security.SE, I finally chose Money.]
It's common to include Guilloché patterns on banknotes, security certificates, and passports to improve security against couterfeiting. I find it hard to believe that modern imaging and printing technology has problems reproducing any image they're given. Is this still an effective deterrent, or is it mostly a legacy of past technology? If it still works, how?
I find it hard to believe that modern imaging and printing technology has problems reproducing any image they're given.
Just because the technology exists doesn't mean your average forger has access to it. Effective forgeries probably involve using the same/similar paper stock and printing process as the original, rather than a scanner and inkjet printer. Creating printing plates isn't trivial and these patterns are one of many security features being used.
A geometric lathe was used for making ornamental patterns on the plates used in printing bank notes and postage stamps. It is sometimes called a guilloché lathe. It was developed early in the nineteenth century when efforts were introduced to combat forgery, and is an adaptation of an ornamental turning lathe. The lathe was able to generate intersecting and interlacing patterns of fine lines in various shapes, which were almost impossible to forge by hand-engraving. They were used by many national mints.
