Currency Security Technologies

Some definitions for technologies, processes, and other terms involved in the security printing industry. See here for the individual trademarked names that have been given to different proprietary versions of these technologies.

The substrate is the material that is being printed on, typically paper.

Overt security devices are meant to be easily seen by the naked eye; the recognizably authentic components of a note (paper quality, texture, among many others)

Covert security devices are hidden within the note, and they’re only detectable with special visual aids (like UV light)

OVDs are optically variable devices; that is, they change their appearance when the viewing angle or type of light is changed. They can change in either color (or be iridescent) or the actual image that is seen. Obviously these are pretty tough to counterfeit.

DOVIDs are diffractive optical variable image devices, like holograms, kinegrams, exelgrams, and pixelgrams. Usually made of multiple layers of thin optical film.

Watermarks have been used against counterfeiting for hundreds of years. A watermark is “a recognizable image or pattern in paper that appears as various shades of lightness/darkness when viewed by transmitted light, caused by thickness or density variations in the paper.”

Digital watermarks are digital images embedded into existing image files printed on the substrate — the embedded files can only be detected with special software.

Void pantographs are hidden images that become apparent when the note is reproduced by a copier or scanner. They are based on the copier’s inability to accurately reproduce screen densities of differing resolutions and dot angles. The naked eye sees an even color density, but the copier reproduces a difference in contrast that brings out the message or symbol.

Microtext is teeny alphanumeric code that is so small that it looks like a continuous line, which can be incorporated into signature lines, portrait outlines, etc.

Intaglio printing, one of the oldest anti-counterfeiting measures. Has a very distinctive look and feel, because the ink lies on top of the paper rather than being pressed into it.

Special-effect inks change their appearance based on any number of circumstances, like viewing angle or addition of heat. They may change from one image to another, or from one color to another. They also may appear and disappear.

Security threads are embedded in the currency paper. They can be visible through windows in the paper, or hidden invisibly within it. They often feature holographic, color-shift, or demetallization (foil strips with windows, essentially) effects. They can even be printed with designs, codes, or text.

Foil elements are exactly what they sound like: foil. On a banknote. They’re flashy and eye-catching, which is good for immediate authentication. They can be holographic, and often include cover security features as well — they may show something entirely different under UV light, for example.

Transparent windows in banknotes are the latest thing in security tech. Basically, it’s “cotton banknote paper with a clearly defined opening that’s sealed with a transparent laminated film.” They can have dynamic effects, patterns, changing colors, you name it.

Micro Optics is also a brand-new technology, which Crane & Co. introduced only a year or two ago. It involves a “micro-lens array interacting with a pre-programmed image array” which produces motion responding to changes in viewing angle.

Other covert security features include laser-written codes only visible under UV light, machine-readable magnetic coding, machine readable electrical conductivity, machine-readable infrared features, UV fluorescence, phosphorescence, and various kinds of laser marking.


Warner, Richard D. and Richard M. Adams II, Introduction to Security Printing. (Pittsburgh: PIA/GATFPress, 2005).

via G&D, “Banknote Security“; Wikipedia, “Watermark“; Crane Currency “Micro Optics

4 Responses to “Currency Security Technologies”
  1. dem says:

    So the “void pantographs” — do they rely upon the participation of the copier/printer manufacturers, or is there something about this technology that works anytime a bill is xeroxed or scanned?

    The kind of software-based protection in the image for this post (where a copier, scanner, or piece of software will recognize that you’re trying to scan currency and will intercept that action in some way) has to involve the consent and participation of the creator of that software, but is this completely voluntary, or does the government or banks have a “big stick” they use to help in the decision making process?

    • catemccrea says:

      The most recently designed notes have some sort of weird technology where if you scan them, the scanner can’t quite read the bill and comes out looking quite strange. I think this kind of tech bypasses the manufacturers of the copiers or printers, and exploits the scanner technology itself. That’s definitely how void pantographs work — they were meant to combat pre-digital counterfeiting that was being done with xerox machines, they basically just made use of a certain aspect of the photocopying process.

      More specifically, they “are based on the copier’s inability to accurately reproduce screen densities of differing resolutions and dot angles. The naked eye sees an even color density, but the copier reproduces a difference in contrast that brings out the message or symbol.”

      I can dig deeper to find out the relationship between photoshop, say, and this kind of enforcement. I’m halfway through a book about security tech. right now (thankfully one that was published in this century) which is definitely going to update the research I have here.

      • dem says:

        I do remember reading (somewhere, ages ago) about how Adobe had agreed to put some sort of currency-recognition into Photoshop to prevent the really basic “scan and print” counterfeiting. It was some tech article that came out with a major update to Photoshop, but I can’t remember when. Maybe within the last 5 years?

        I remember it gave me trouble once when I wanted to scan a $20 to print as prop money. Though I also clearly got around it somehow, as the roll of prop $20s on my office desk attests…

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