Watermarking Systems and Methods

Abstract

Various improvements and applications for digital watermarking technology are detailed. One concerns techniques for making watermarks resistant to malicious attacks. Another involves using digital watermarking with ID cards and credentials, such as a watermarked driver's license conveying a user's cryptographic PKI. Still another uses digital watermarks in connection with automated compliance audits for corporate users of electronic content. A variety of other technologies are also detailed.

1 - 7 . (canceled) 
     
     
         8 . An object including a substrate printed with a pattern of metallic ink, the patterned metallic ink defining a diffraction grating at a microwave frequency. 
     
     
         9 . The object of  claim 8  in which the substrate has first and second sides, the first side including the pattern of metallic ink, the second side comprising a reflective plane. 
     
     
         10 . The object of  claim 9  in which the reflective plane comprises metal. 
     
     
         11 . The object of  claim 8 , further comprising a reflective material disposed parallel to, but spaced apart from, said pattern of metallic ink. 
     
     
         12 . The object of  claim 8 , wherein the object further conveys identification information relating to a person. 
     
     
         13 . An identity card according to  claim 12 . 
     
     
         14 . A method comprising printing a substrate with metallic ink to thereby define a microwave diffraction grating, and also printing said substrate to convey identification information relating to a person. 
     
     
         15 . The method of  claim 14  that further includes forming a reflective layer disposed parallel to, but spaced apart from, said microwave diffraction grating. 
     
     
         16 . An object including a substrate printed with a pattern of metallic ink, the patterned metallic ink defining a diffraction grating at a microwave, infrared, or ultraviolet, but not visible, wavelength.