Digital watermarking and banknotes

Machine-readable data is digitally watermarked into banknotes. Such watermarking can be optically sensed and detected by various devices. In response, such devices can intervene to prevent banknote reproduction. This arrangement addresses various problems, e.g., the use of digital image editing tools to circumvent prior art banknote anti-copy systems. In some embodiments, visible structures characteristic of banknotes are also detected (e.g. by pattern recognition analysis of image data), and reproduction can be halted if either the visible structures or the digital watermark data are detected. In other embodiments, automatic teller machines that accept, as well as dispense, banknotes can check for the presence of digitally watermarked data to help confirm the authenticity of banknotes. In other embodiments, scanners, printers and photocopiers can be provided with digital watermarking capabilities so that image data, or printed output, produced by such devices includes digital watermark data, permitting subsequent identification of the particular device used. The digital watermarking can be effected by making slight alterations to ink color, density, etc., or by texturing the microtopology of the banknote surface. Some embodiments effect the watermarking by modulating the width or placement of component lines that form line art imagery on the banknote.