Numerous variations exist, including printing the marks using a raster of lines in one direction on a background of lines in another direction, or using fine line patterns that alias into a visible moire pattern when copied. Features smaller than the resolution will also not be reproduced. It will also not be perfectly aligned with the directions of the document, causing aliasing. A scanner or photocopier will act as a low-pass filter on the original image, blurring edges slightly. For that, it seems to be the way to go to have two micro-dotted halftone images in which the underlying one has a different frequency then the one that renders the text. This makes it possible to see a pattern that had been invisible. Void pantographs work by exploiting the limitations and features of copying equipment. Apparently these are called Void Pantographs and some printers can even put them on any page printed - mine can't. 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'). In addition, human vision is sensitive to luminance contrast ratio. Features smaller than the resolution will also not be reproduced. Void pantographs work by exploiting the limitations and features of copying equipment. It will also not be perfectly aligned with the directions of the document, causing aliasing. The void pantograph includes a foreground portion based on a region of an image that is defined using a predetermined filter, and a background portion based on another region of the image that is. Void pantographs work by exploiting the limitations and features of copying equipment. Typically they spell out 'void', 'copy', 'invalid' or some other indicator message. Micro lettering In case of material/chemical alteration the Micro lettering on the instrument will get distorted. UV Logo Help the banks identifying the fake instruments by running them through UV lamp and looking for UV logo. Normally these are invisible to the eye, but become obvious when the document is photocopied. Void Pantograph Visible on a photo copy of 2010 standard compliant instruments. In security printing, void pantograph refers to a method of making copy-evident and tamper-resistant patterns in the background of a document.

Void pantograph image