Method for determining a printer's signature and the number of dots per inch printed in a document to provide proof that the printer printed a particular document

Abstract

A method for assigning unique printer resolutions or signatures, i.e., a unique number of dots per inch, to a class, or models of printers or lines of postage meters. 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 on document or the postal indicia has the correct resolution. The foregoing would be able to detect an image or postal indicia that was scanned into a computer and printed with a printer that did not have the number of dots per inch specified in the image or postal indicia.

What is claimed is: 
     
       1. A method for determining whether an image on a substrate has a specified number of dots per inch, said method includes the steps of:
 specifying that the image on the substrate will be printed with n plus m dots per inch; 
 rotating a an ink jet head having n nozzles per inch about a Y 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 the image 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; 
 comparing the number of dots per inch in the analyzed image with the number of dots per inch stored in the specified image to determine if they have the same number of dots per inch; 
 analyzing the image to determine if the image has the specified dots per inch along the X and Y axis; and 
 comparing the number of dots per inch along the X and Y axis in the analyzed image with the number of dots per inch along the X and Y axis stored in the image to determine if they have the same number of dots per inch. 
 
     
     
       2. The method claimed in  claim 1 , further including the step of:
 encoding the number of dots per inch that is specified to be printed into the image. 
 
     
     
       3. The method claimed in  claim 2 , wherein the image is a postal indicia indicium. 
     
     
       4. The method claimed in  claim 2 , further including the step of:
 encrypting the number of dots per inch indicated in the image. 
 
     
     
       5. The method claimed in  claim 2 , wherein the image is a graphic. 
     
     
       6. The method claimed in  claim 1 , further including the steps of:
 positioning individual dots about the X axis to build an the image. 
 
     
     
       7. The method claimed in  claim 1 , further including the steps of:
 specifying the spacing of dots about the X,axis to create an the image. 
 
     
     
       8. A method for printing an image on a substrate having a surface including a first axis and a second axis with a specified number of dots per inch in at least one of the first and second axes, the substrate moving in the direction of the first axis, said method comprising:
 obtaining data for determining a first specified number of dots per inch that the image on the substrate will be printed with in the direction of the second axis;   rotating an array number of pixel generating elements per inch about an axis orthogonal to the substrate surface by an angle to produce the image on the substrate having the first specified number of dots per inch in the direction of the second axis, wherein the specified number of dots per inch is larger than the array number;   storing in the image that the image will be printed with the first specified number of dots per inch in the direction of the second axis;   analyzing the image to determine a number of dots per inch in the direction of the second axis; and   comparing the determined number of dots per inch in the direction of the second axis in the analyzed image with the first specified number of dots per inch in the direction of the second axis stored in the image to determine if they have the same number of dots per inch.   
     
     
       9. The method of claim 8, further comprising:
 obtaining data for determining a second specified number of dots per inch that the image on the substrate will be printed with in the direction of the first axis;   configuring a timing controller for triggering printing of pixels to generate the image with the second specified number of dots per inch in the direction of the first axis; and   storing in the image that the image will be printed with the second specified number of dots per inch in the direction of the first axis.   
     
     
       10. The method of claim 8, wherein:
 the angle is between approximately 10 and 20 degrees.   
     
     
       11. The method of claim 8, wherein:
 the image is a postal indicium.   
     
     
       12. The method of claim 8, further comprising:
 encrypting the first specified number of dots per inch stored in the image.   
     
     
       13. The method of claim 8, further comprising:
 positioning individual dots about the first axis to build the image.   
     
     
       14. The method of claim 8, further comprising:
 specifying the spacing of dots parallel to the first axis to create the image.