Copy Detection Using Line Art Features and Encoded Signals

An image processing method for authenticating a value document comprising:

• obtaining an image depicting a value document, in which the value document comprises a substrate comprising printing thereon, in which the printing comprises a line art feature comprising a plurality of lines associated with one or more line frequencies, the line art feature comprising an encoded signal carried by modulations to the plurality of lines, in which the encoded signal comprises a synchronization component and a message component, and in which the printing is printed with a first spot color ink;
• analyzing the image to decode the message component from the encoded signal, the message component indicating data associated with expected frequency domain locations of one or more line frequencies;
• transforming the image into a frequency domain, and determining frequency domain locations for the one or more line frequencies in the frequency domain, said determining frequency domain locations yielding determined locations of the one or more line frequencies;
• and
• determining whether one or more of the expected frequency domain locations of the one or more line frequencies and one or more frequency domain locations of the determined locations of the one or more line frequencies coincide.

A printed object comprising:

• a substrate;
• and
• printing on the substrate, the printing arranged in a 2D pattern to convey a digital watermark signal, the digital watermark signal comprising a plural-bit payload, the printing comprising a white ink/gloss varnish mixture, in which the white ink/gloss varnish mixture comprises 55%-70% by volume or weight of white ink and 45%-30% by volume or weight of gloss varnish, in which under white light or ambient illumination, a layer of white ink/gloss varnish mixture/substrates appears lighter than the substrate, and in which under ultraviolet illumination, the layer of white ink/gloss varnish mixture/substrates appears darker relative to the substrate,
• wherein the digital watermark signal comprises a signal polarity, and under white light or ambient illumination, the digital watermark signal is interpreted as positive polarity, and under ultraviolet illumination the digital watermark signal is interpreted as negative polarity.