Method for determining a printer's signature to provide proof that the printer printed a particular document

Abstract

The number of dots per inch or resolution may be specified within a image on a document or within a postal indicia and later checked to determine if the image or document or the postal indicia has the correct resolution. The foregoing is accomplished by specifying that the image on the substrate will be printed with n plus m dots per inch; rotating a ink jet head having n nozzles per inch about a axis parallel to a substrate by an angle θ so that the ink jet head will produce an image on the substrate having (n/cos θ) dots per inch; storing in a data center that the specified image will be printed with (n/cos θ) dots per inch; analyzing the image to determine if the image has (n/cos θ) dots per inch; and comparing the number of dots per inch in the analyzed image with the number of dots per inch stored for the specified image to determine if they have the same number of dots per inch.

Dependencies are inferred from the claim text.