Digital Authentication with Digital and Analog Documents

Abstract

A watermark embedder transforms a media signal from its perceptual domain to frequency domain regions and embeds a hash of data from one frequency domain region into a watermark in another frequency domain region. Alternatively, it encodes instances of the same message into the frequency domain regions. To detect alteration of the media signal, a watermark decoder transforms a suspect signal into the frequency domain regions, extracts the watermark message from a first frequency domain region and compares it with a reference derived from another frequency domain region. The reference signal is either a hash computed from the other frequency domain region of the watermarked signal, or another instance of the same message embedded into the other frequency domain region. The decoder can be used to detect alteration of the signal, such as alteration that occurs with reproduction (printing, scanning, copying, D/A-A/D conversion, etc.), compression, cropping or swapping of media signal content, etc.

1 . Apparatus which authenticates a digital representation of an object from which an analog form may be made, the apparatus comprising: 
 an authenticator which uses first information in a first portion of the digital representation to produce first authentication information, the first information also being obtainable from a third portion of the analog form that is made from the first portion; and    an incorporator which incorporates the first authentication information in a second portion of the digital representation, the authentication information also being obtainable from a fourth portion of the analog form that is made from the second portion.    
     
     
         2 . The apparatus set forth in  claim 1  wherein: 
 the digital representation includes items of data, each item has more significant components and less significant components, the first portion is certain more significant components of the item, and the second portion is certain less significant components of the item.    
     
     
         3 . The apparatus set forth in  claim 2  wherein: 
 the items are pixels and the components are bits in the pixels.    
     
     
         4 . The apparatus set forth in  claim 2  wherein: 
 the items are signal samples and the components are bits in the signal samples.    
     
     
         5 . The apparatus set forth in  claim 2  wherein: 
 the items are DCT blocks containing frequency coefficients and the components are frequency coefficients in the DCT block.    
     
     
         6 . The apparatus set forth in  claim 1  wherein: 
 the digital representation includes an image, the first portion is a first specific region of the image, and the second portion is a second specific region of the image.    
     
     
         7 . The apparatus set forth in  claim 1  wherein: 
 the first portion is vector data in the object.    
     
     
         8 . Apparatus which authenticates a digital representation of an object, the digital representation including frequency components and the apparatus comprising: 
 an authenticator which uses first information in more significant frequency components of the components to produce first authentication information; and    an incorporator which incorporates the first authentication information into less significant frequency components of the components that do not overlap the more significant frequency components.    
     
     
         9 . The apparatus set forth in  claim 8  wherein: 
 the frequency components are coefficient values that represent significant frequency components that are computed by a perception model.    
     
     
         10 . The apparatus set forth in  claim 9  wherein: 
 the perception model is an auditory perception model.    
     
     
         11 . The apparatus set forth in  claim 9  wherein: 
 the perception model is a visual perception model.    
     
     
         12 . The apparatus set forth in  claim 8  wherein: 
 the frequency components are contained in DCT blocks.    
     
     
         13 . The apparatus set forth in  claim 8  wherein: 
 the first authentication information is a digital signature.    
     
     
         14 . The apparatus set forth in  claim 8  wherein: 
 the first authentication information is a secure hash code.    
     
     
         15 . The apparatus set forth in  claim 8  wherein: 
 the first authentication information is a cryptographic code.    
     
     
         16 . The apparatus set forth in  claim 8  wherein: 
 the first authentication information is a hash code.