Method and apparatus for image authentication

A digital image authenticator, the authenticator receiving data representing a digital image to be authenticated and a digital signature for the original image, the authenticator comprising:

• means for generating coefficients from the data representing the image to be authenticated, said means for generating coefficients representing the data representing the image into a plurality of image blocks;
• means for extracting invariant features for the original image from the digital signature;
• and
• an authentication comparator, said authentication comparator receiving the coefficients from the generating means, grouping the plurality of image blocks into at least one image block pair and generating invariant features for the image to be authenticated from a relationship between corresponding coefficients which are at least partially defined by the polarity of the difference of discrete cosine coefficients and the magnitude of the difference of discrete cosine transform coefficients of corresponding coefficient locations in the at least one image block pair, said authentication comparator comparing the generated invariant features of the present image to corresponding invariant features from the original image and providing a signal indicative of an authentication failure if the corresponding invariant features do not substantially match.

A method for generating an invariant feature for a digital image comprising the steps:

• partitioning the image into a plurality of image blocks;
• assigning at least one image block pair from said plurality of image blocks;
• extracting coefficients for pixels in said at least one image block pair;
• determining an invariant relationship between corresponding coefficients of said at least one image block pair, said relationship being at least partially defined by the polarity of the difference and the magnitude of the difference of said corresponding coefficients.

A method for authenticating a present image based on a signature generated from invariant features of an original image, comprising the steps:

• partitioning the present image into a plurality of image block pairs;
• extracting coefficients for the image block pairs;
• generating invariant features for the present image to be authenticated from a relationship between corresponding coefficients of at least one image block pair, said relationship being at least partially defined by the magnitude of the difference of said corresponding coefficients;
• extracting invariant features for the original image from the signature;
• comparing the invariant features of the present image to corresponding invariant features of the original image;
• and
• providing a signal indicative of an authentication failure if the corresponding invariant features do not substantially match.