Abstract: A document authentication method uses a watermark added in a printed document to detection possible alterations made to the document after it was printed. First, a visible watermark in the form of a dot pattern is overlapped with an original digital image. The watermarked image is printed out as a halftone image at a first resolution. The watermark in the printed document appears as a light gray shade. Later, the printed document is scanned back using a grayscale scan at a resolution higher than the first resolution. In the scanned image, altered areas would appear flat (lacking intensity variation) whereas unaltered areas will have relatively large density variations due to the watermark dots and the fact that the image was halftone printed at a lower resolution. Alternations are detected by identifying flat areas within the image using a combination of flat block detection and a multiple thresholds method.

Abstract: A document authenticating method is disclosed by which numerous small-sized two-dimensional barcode stamps are generated and placed in a distributed manner on a printed document. The small-sized barcode stamps collectively encode the content of the document to be used for document authentication. In one example, the stamp size is about ¼ by ¼ inches or less and the tile size for the stamps is 4 by 4 pixels at a resolution of 400 dpi. The document is segmented into segments each containing a paragraph or a line of text. For each segment, a set of barcode stamps encoding the authentication data for the segment is placed in the vicinity of the segment. They may be placed in the empty space in the last line of each paragraph, in the empty space between adjacent paragraphs, or at the beginning or end of each line.

Abstract: An apparatus and method for deskewing a scanned printed document is described. The original printed document is scanned with the scanner to obtain a first digital image, which contains skew (rotation) with respect to the original printed document. The first digital image is digitally flipped around a centerline to obtain a second digital image, which is printed to generate a second printed document. The second printed document is scanned using the same scanner to obtain a third digital image, which contains skew errors with respect to the second printed document. The third digital image is digitally flipped around the centerline to obtain a final digital image, which is substantially free of the skew introduced by the scanner.

Abstract: A document authentication method uses a watermark added in a printed document to detection possible alterations made to the document after it was printed. First, a visible watermark in the form of a dot pattern is overlapped with an original digital image. The watermarked image is printed out as a halftone image at a first resolution. The watermark in the printed document appears as a light gray shade. Later, the printed document is scanned back using a grayscale scan at a resolution higher than the first resolution. In the scanned image, altered areas would appear flat (lacking intensity variation) whereas unaltered areas will have relatively large density variations due to the watermark dots and the fact that the image was halftone printed at a lower resolution. Alternations are detected by identifying flat areas within the image using a combination of flat block detection and a multiple thresholds method.

Abstract: A document authentication method uses a watermark added in a printed document to detection possible alterations made to the document after it was printed. First, a visible watermark in the form of a dot pattern is overlapped with an original digital image. The watermarked image is printed out as a halftone image at a first resolution. The watermark in the printed document appears as a light gray shade. Later, the printed document is scanned back using a grayscale scan at a resolution higher than the first resolution. In the scanned image, altered areas would appear flat (lacking intensity variation) whereas unaltered areas will have relatively large density variations due to the watermark dots and the fact that the image was halftone printed at a lower resolution. Alternations are detected by identifying flat areas within the image using a combination of flat block detection and a multiple thresholds method.

Abstract: A document authenticating method is disclosed by which numerous small-sized two-dimensional barcode stamps are generated and placed in a distributed manner on a printed document. The small-sized barcode stamps collectively encode the content of the document to be used for document authentication. In one example, the stamp size is about ¼ by ¼ inches or less and the tile size for the stamps is 4 by 4 pixels at a resolution of 400 dpi. The document is segmented into segments each containing a paragraph or a line of text. For each segment, a set of barcode stamps encoding the authentication data for the segment is placed in the vicinity of the segment. They may be placed in the empty space in the last line of each paragraph, in the empty space between adjacent paragraphs, or at the beginning or end of each line.

Abstract: A document authenticating method is disclosed by which numerous small-sized two-dimensional barcode stamps are generated and placed in a distributed manner on a printed document. The small-sized barcode stamps collectively encode the content of the document to be used for document authentication. In one example, the stamp size is 1 cm by 1 cm and the tile size for the stamps is 4 by 4 pixels at a resolution of 400 dpi. A total of approximately 80 such small barcode stamps are placed on the page to form a pattern that resembles a border on one or more sides of the page. In one particular example, the stamps are placed on all four sides of the page to form a frame. Such a stamp layout minimizes undesirable visual effect and can create a decorative effect. Small-sized stamps also allow reduced tile sizes and increased information density.

Abstract: A document authentication method uses a watermark added in a printed document to detection possible alterations made to the document after it was printed. First, a visible watermark in the form of a dot pattern is overlapped with an original digital image. The watermarked image is printed out as a halftone image at a first resolution. The watermark in the printed document appears as a light gray shade. Later, the printed document is scanned back using a grayscale scan at a resolution higher than the first resolution. In the scanned image, altered areas would appear flat (lacking intensity variation) whereas unaltered areas will have relatively large density variations due to the watermark dots and the fact that the image was halftone printed at a lower resolution. Alternations are detected by identifying flat areas within the image using a combination of flat block detection and a multiple thresholds method.

Abstract: An apparatus and method for deskewing a scanned printed document is described. The original printed document is scanned with the scanner to obtain a first digital image, which contains skew (rotation) with respect to the original printed document. The first digital image is digitally flipped around a centerline to obtain a second digital image, which is printed to generate a second printed document. The second printed document is scanned using the same scanner to obtain a third digital image, which contains skew errors with respect to the second printed document. The third digital image is digitally flipped around the centerline to obtain a final digital image, which is substantially free of the skew introduced by the scanner.