Embedded information in printed documents can be used for a number of applications such as authentication of document content, proof of ownership, and identification of the printer that produced documents. One approach is to embed information in the halftone portions at the printer mechanism-level. The advantage of printer mechanism-level information embedding is that information is directly embedded in printed documents without any further steps that might alter the intended information. In this paper, we describe a printer mechanism-level information embedding and detection scheme as an extension to our previous result. An information bit is embedded by changing the position of a dot to be developed and these information bits are grouped together to be robust to noise caused by various reasons. The previous detection algorithm is modified to improve the detection rate of embedded information in printed documents. Consequently, we are now able to embed information using a reduced level of dot shift, which better maintains the halftone image quality. The experimental results show that our proposed scheme is feasible to embed and detect information in printed documents.
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