6. A method implemented in a data processing system for authenticating a printed document, the printed document including a hierarchical barcode stamp and a document image printed on a front side of a recording medium and first barcode stamps printed on a front or back side of the same recording medium, the method comprising: (a) obtaining a front side image and a back side image from the printed document; (b) extracting the document image and the hierarchical barcode stamp from the front side image; (c) processing the document image extracted in step (b) to obtain first processed data; (d) extracting a first code from the hierarchical barcode stamp extracted in step (b); (e) reading and decoding the first barcode stamps in the front side image and/or the back side image to obtain second processed data encoded therein; (f) calculating a second code from the second processed data; (g) comparing the first code and the second code to determine whether the first barcode stamps have been altered; and (h) comparing first processed data and second processed data to determine whether the printed document has been altered.
6. A method implemented in a data processing system for authenticating a printed document, the printed document including a hierarchical barcode stamp and a document image printed on a front side of a recording medium and first barcode stamps printed on a front or back side of the same recording medium, the method comprising: (a) obtaining a front side image and a back side image from the printed document; (b) extracting the document image and the hierarchical barcode stamp from the front side image; (c) processing the document image extracted in step (b) to obtain first processed data; (d) extracting a first code from the hierarchical barcode stamp extracted in step (b); (e) reading and decoding the first barcode stamps in the front side image and/or the back side image to obtain second processed data encoded therein; (f) calculating a second code from the second processed data; (g) comparing the first code and the second code to determine whether the first barcode stamps have been altered; and (h) comparing first processed data and second processed data to determine whether the printed document has been altered. 9. The method of claim 6 , wherein step (d) comprises: (d1) generating a barcode stamp element from the hierarchical barcode stamp, wherein the hierarchical barcode stamp comprises the barcode stamp element being repeated in accordance with a pre-defined pattern; and (d2) decoding the barcode stamp element to obtain the first code.