Methods for marking images

Abstract

An image is marked by making slight changes to pixel values. These changes are essentially imperceptible on human scrutiny, but detectable by computer analysis. Such markings have applications in identifying ownership of images (including video), and also in device control (e.g., triggering a “do not copy” response in suitably configured hardware and software systems).

I claim:  
     
         1 . A method for imparting a watermark onto a digitized image comprising the steps of: 
 providing said digitized image comprised of a plurality of pixels, wherein each of said pixels includes brightness data that represents a brightness of at least one color; and    multiplying said brightness data associated with at least one of said pixels by a predetermined brightness multiplying factor, said brightness multiplying factor, “mf”, is selected from the group consisting of (0.9<=“mf”<1), and (1<“mf”<=1.1).    
     
     
         2 . A method as recited in  claim 1 , wherein each pixel is associated with a brightness data value that represents a brightness of a monochrome color.  
     
     
         3 . A method as recited in  claim 1 , wherein each pixel is associated with a plurality of brightness data values.  
     
     
         4 . A method as recited in  claim 3 , wherein said plurality of brightness data values represents brightness of a red, green and blue color.  
     
     
         5 . A method as recited in  claim 1 , wherein said watermark has an invisibility classification level of undetectably invisible.  
     
     
         6 . A method as recited in  claim 1 , wherein said brightness multiplying factor has a relationship with a number taken from a random number sequence.  
     
     
         7 . A method as recited in  claim 6 , wherein said relationship is a linear remapping to provide a desired modulation strength.  
     
     
         8 . A method as recited in  claim 6 , wherein said modulation strength is 10%.  
     
     
         9 . A method as recited in  claim 6 , wherein each of said pixels has a row and a column location in an array representing said digitized image, and wherein said brightness multiplying factor employs a different sequential combination of numbers from said random number sequence in sequential correspondence to said row and column location.  
     
     
         10 . A method as recited in  claim 6 , wherein said random number sequence is generated employing a National Standard Data Encryption Algorithm.  
     
     
         11 . A method as recited in  claim 6 , wherein said sequence is formed from a plurality of watermarking parameters.  
     
     
         12 . A method as recited in  claim 11 , wherein said watermarking parameters provide the watermark with at least one property of a robust invisible watermark.  
     
     
         13 . A method for generating a watermarked image wherein a watermark is imparted onto a digitized image having a plurality of original elements having original brightnesses, said method comprising the steps of: 
 providing a digitized watermarking plane comprising a plurality of watermarking elements, each having a watermark brightness multiplying factor and having one-to-one correspondence with said original elements; and    producing a watermarked image by multiplying said original brightness of each of said original elements by said brightness multiplying factor of a corresponding one of said watermark elements wherein said watermark is invisible.    
     
     
         14 . A method as recited in  claim 13 , in which said brightness multiplying factors are in a range of 0.9 to 1.1.  
     
     
         15 . A method as recited in  claim 13 , in which said original image forms an original plane and said watermarking image forms a watermarking plane being smaller than said original plane, said method further comprising the step of extending said watermarking plane by tiling such that said watermarking plane at least covers said original plane.  
     
     
         16 . A method as recited in  claim 15 , further comprising the step of truncating said watermarking plane such that said watermarking plane covers said original plane, upon determining that said watermarking plane extends beyond said original plane.  
     
     
         17 . A method as recited in  claim 15 , wherein the watermarking plane is produced by employing an inverse discrete Fourier transform.  
     
     
         18 . A method as recited in  claim 13 , wherein each of said original elements include a plurality of brightness values corresponding to a red, a green and a blue color component.  
     
     
         19 . A method for imparting a watermark onto a digitized image comprising the steps of: 
 providing said digitized image comprised of a plurality of pixels, wherein each of said pixels includes brightness data that represents a brightness of at least one color; and    multiplying said brightness data associated with at least one of said pixels by a predetermined brightness multiplying factor in the range of 0.9 to 1.1,    wherein said brightness multiplying factor has a relationship with a number taken from a random number sequence, said relationship is a linear remapping to provide a desired modulation strength, and said modulation strength is less than 0.5 percent.    
     
     
         20 . A method for imparting a watermark onto a digitized image comprising the steps of: 
 providing said digitized image comprised of a plurality of pixels, wherein each of said pixels includes brightness data that represents a brightness of at least one color; and    multiplying said brightness data associated with at least one of said pixels by a predetermined brightness multiplying factor in the range of 0.9 to 1.1,    wherein said brightness multiplying factor has a relationship with a number taken from a random number sequence, said relationship is a linear remapping to provide a desired modulation strength, said sequence is formed from a plurality of robust watermarking parameters, and said parameters comprise a cryptographic key, two coefficients and an initial value of said random number generator.