Security printing is the field of the printing industry that deals with the printing of items such as banknotes, cheques, passports, tamper-evident labels, security tapes, product authentication, stock certificates, postage stamps, and identity cards. The main goal of security printing is to prevent forgery, tampering, or counterfeiting. More recently many of the techniques used to protect these high-value documents have become more available to commercial printers, whether they are using the more traditional offset and flexographic presses or the newer digital platforms. Businesses are protecting their lesser-value documents such as transcripts, coupons and prescription pads by incorporating some of the features listed below to ensure that they cannot be forged or that alteration of the data cannot occur undetected. A number of technical methods are used in the security printing industry. Security printing is most often done on security paper, but it can also occur on plastic materials.
Features detectable by humans Secured documents, such as banknotes, use visible and tactile features to allow humans to verify their authenticity without tools. The European Central Bank (ECB) recommends feel, look, and tilt: First check the tactility of the banknote (including the substrate), then look at the optical design and finally the characteristics of certain optical features when tilting the banknote in relation to the incident light.
In general, the introduction of a new banknote series is accompanied by information campaigns describing the design and the security features. Several central banks also provide mobile apps explaining the characteristics by interactive methods and enrich them by animated effects. In general, they use the camera of a mobile device to explain the features of a presented banknote. As they do not support the direct verification of authenticity they also work with simple printouts or screen displays.
SwissBanknotes from the Swiss National Bank for the Swiss franc with animated effects MalawiKwacha from the Reserve Bank of Malawi for the Malawian kwacha with simulations of tilting and tactility as well as interactive effects by enhanced reality SARBCurrency from the South African Reserve Bank for the South African rand as an offline application explaining the security features by enhanced reality Lilangeni from the Central Bank of Eswatini for the Swazi lilangeni with simulations of tilting and tactility as well as interactive effects by enhanced reality
Substrate
Paper The substrate of most banknotes is made of paper, almost always from cotton fibres for strength and durability; in some cases linen or specially coloured or forensic fibres are added to give the paper added individuality and protect against counterfeiting. Paper substrate may also include windows based on laser-cut holes covered by a security foil with holographic elements. All of this makes it difficult to reproduce using common counterfeiting techniques.
Polymer Some countries, including Canada, Nigeria, Romania, Mexico, Hong Kong, New Zealand, Israel, Singapore, Malaysia, United Kingdom, and Australia, produce polymer (plastic) banknotes, to improve longevity and to make counterfeiting more difficult. Polymer can include transparent windows, diffraction grating, and raised printing.
Format Most currencies use different dimensions of length, width, or both for the different denominations, with smaller formats for the lower denominations and larger formats for the higher denominations, to hinder reuse of the substrate with embedded security features for counterfeiting higher denominations. Blind and visually impaired people may also rely on the format for distinguishing between the denominations.
Visible security features
Watermark True watermark A true watermark is a recognizable image or pattern in paper that appears lighter or darker than surrounding paper when viewed with a light from behind the paper, due to paper density variations. A watermark is made by impressing a water coated metal stamp or dandy roll onto the paper during manufacturing. Watermarks were first introduced in Bologna, Italy in 1282; as well as their use in security printing, they have also been used by paper makers to identify their product. For proofing the authenticity, the thinner part of the watermark will shine brighter with a light source in the background and darker with a dark background. The watermark is a proven anti-counterfeit technology because most counterfeits only simulate its appearance by using a printing pattern.
Simulated watermark Printed with white ink, simulated watermarks have a different reflectance than the base paper and can be seen at an angle. Because the ink is white, it cannot be photocopied or scanned. A similar effect can be achieved by iriodin varnish which creates reflections under certain viewing angles only and is transparent otherwise. Watermarks are sometimes simulated on polymer currency by printing an according pattern, but with little anti-counterfeiting effect. For example, the Australian dollar has its coat of arms watermarked on all its plastic bills. A Diffractive Optical Element (DOE) within the transparent window can create a comparable effect but requires a laser beam for its verification.
See-through register See-through registers are based on complementary patterns on the obverse and reverse of the banknote and constitute a complete pattern under backlight conditions. Examples are the D of the Deutsche Mark (1989 series, BBk III) and the value number of the first series of euro banknotes (ES1). Counterfeiting is difficult because the printing registration requires an extremely high printing accuracy on both sides and minor deviations are easily detectable.
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