Void pantograph
method of security printing aimed at foiling photographic duplication
In security printing, void pantograph refers to a method of making copy-evident and tamper-resistant patterns in the background of a document. Normally these are invisible to the eye, but become obvious when the document is photocopied. Typically they spell out "void", "copy", "invalid" or some other indicator message.
Void pantographs work by exploiting the limitations and features of copying equipment. A scanner or photocopier will act as a low-pass filter on the original image, blurring edges slightly. It will also not be perfectly aligned with the directions of the document, causing aliasing. Features smaller than the resolution will also not be reproduced. In addition, human vision is sensitive to luminance contrast ratio. This means that if a grey region consists of a grid of very small dark dots the filtering will produce a lighter grey, while a region of larger dots will be affected differently ("big-dot-little-dot"). This makes it possible to see a pattern that had been invisible.
“Void pantograph” enters the record as method of security printing aimed at foiling photographic duplication. Crown Archives preserves that source wording while asking what Void, pantograph and method can confirm, complicate or overturn.
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Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Sep 16, 2026. The linked authority identifier is Q17087142. None of the 0 selected statements returned an explicit reference.
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This entry incorporates text from “Void pantograph” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.