Digital watermarks for checking authenticity of printed objects
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United States of America Patent
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Jul 17, 2007
Grant Date -
Jul 25, 2002
app pub date -
Aug 23, 2001
filing date -
Jan 24, 2001
priority date (Note) -
In Force
status (Latency Note)
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Abstract
The invention provides methods for embedding digital watermarks for authentication of printed objects, and corresponding methods for authenticating these objects. One aspect of the invention is a method of embedding a digital watermark in a digital image to be printed on an object. The method embeds an auxiliary signal in the digital image so that the auxiliary signal is substantially imperceptible, yet machine readable. It converts the image to a halftone image using an inherently unstable halftone screen structure that is likely to cause ink flow errors when reproduced. The errors introduced by reproducing the unstable halftone screen structure incorrectly are automatically detectable by reading the auxiliary signal.
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