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9 February 2006 New applications of modulated digital images in document security
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In previous work we have demonstrated that selective masking, or modulation, of digital images can be used to create documents and transparent media containing covert or optically variable, overt images. In the present work we describe new applications and techniques of such "modulated digital images" (MDI's) in document security. In particular, we demonstrate that multiple hidden images can be imperceptibly concealed within visible, host images by incorporating them as a new, half-tone, printing screen. Half-toned hidden images of this type may contain a variety of novel features that hinder unauthorized copying, including concealed multiple images, and microprinted-, color-, and various fadeeffects. Black-and-white or full color images may be readily used in this respect. We also report a new technique for the embossing of multiple, covert- or optically variable, overt-images into transparent substrates. This method employs an embossing tool that is prepared using a combination of electron beam and greytone lithography. Two approaches may be used: (i) a double-sided "soft" emboss into curable, transparent, lacquer layers, and (ii) a single-sided "hot" emboss in which multiple, dithered images consisting of distinctly-sloped microprisms are impressed into the substrate. Technique (ii) requires a novel, electron-beam-originated master dye.
© (2006) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Robert A. Lee, Patrick W. Leech, Lawry D McCarthy, and Gerhard F. Swiegers "New applications of modulated digital images in document security", Proc. SPIE 6075, Optical Security and Counterfeit Deterrence Techniques VI, 60750C (9 February 2006);


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