<title>New alteration detecting technique for printed documents using dot pattern watermarking</title>

Abstract

This paper proposes a unique watermarking technique for printed documents by superposing dot pattern blocks on backgrounds of the document images. The dot pattern block contains information, but it is not visually distracting as the printed documents look as if uniform dot patterns are superposed on the background. The dots in the dot pattern block are lined up to a certain direction so that these dots generate 2-D wavelet in a scanned image of the printed documents. We have described the difference of symbols "0" and "1" as the difference of wavelet direction, and each wavelet is detected by 2-D Gabor filter, which makes the symbol detection error rate very low. In addition, accuracy of detection is not affected by format or layout of documents. Alteration detection can be achieved by embedding original document image feature into document image itself as alteration detection data. When watermark is extracted, the alteration detection data and the image feature of scanned image, are compared to determine if alterations are made or not.

A Feature Extracting Method for Tamper Detection in Printed Documents

“…Third, using the feature of the paper has been proposed. Suzaki and et al has proposed the watermarking technique for printed documents by superposing dot pattern blocks on backgrounds of the document image (Suzaki, 2003). Figure 1 shows the overview of our document verification system.…”

A watermark embedding and extracting method for printed documents

“…Also, the recorded data may become unreadable when recorded areas are stained or damaged. This paper proposes a new watermarking technique that embeds watermark information (digital data) in printed documents by inserting mesh patterns in a document background [10]. The background comprises mesh patterns in which microdots are evenly assigned, with equal spaces between them, and information is embedded by blending mesh patterns into the background.…”