Security Ink Visualization

Security inks not visible by human eyes are often used to avoid currency and document counterfeiting.   

Images of first and second series 10 euro bill and a couple of pages of a Latvian passport were taken using a MSLED-RGBN-2-4 illuminator with four spectral channels (red (620 nm), green (520 nm), blue (470 nm), near-infrared (850 nm)) and a monochrome 4.2 MP camera, MSC2-M42-1-A. The images obtained using red, green and blue light were merged to form a typical color (RGB) image.

For the first series 10 euro bill the image of an arch and the number 10 on the banknote was partially printed using infrared (IR) security inks. The second series bill features a larger section of the arch without the number 10 on the right side.  Similarly, first page of the Latvian passport features an image of a man that is partially printed with IR ink while the second page reveals the national anthem notes.

Using the NIR illumination at 850 nm, the invisible features to the naked eye are unveiled. Note how the lack of visible light in NIR images hides all the features printed using visible spectrum inks.