ABSTRACT
With the fast development of Internet and the application of digital works, people
have enjoyed the convenience and faced the risks of being verified. Digital watermark is
an effective way to protect the copyright, which is a mutual way now. With the fast
development of info-tech and high quality image processing equipments, especially
laser printers, high precision color inkjet and scanners, life has become much easier. But
at the same time, someone can easily verify and fake the certificates, invoices and
documents. It is of great importance to study an algorithm against printing and
scanning.
The paper studies on the application of digital watermark in printing security area
from both theoretical and practical sides. The method has deep theory foundation
through double random phase modulation encryption holographic technology, Fourier
encryption holographic technology, printing technology. Firstly, two digital watermark
algorithm were proposed, which laid a good basis for printing watermark algorithm
design. Then the constant characteristics is extracted for analysis, after analysis,
anti-printing algorithms were proposed. The main idea of this paper is as follows:
1. On the basis of principle of digital watermark and classification and modes,
Analysis of the digital watermarking and printing watermarking difference is done to
meet the requirement of printing watermark system.
2. A new watermark algorithm was proposed with the analysis of DWT theory.
This algorithm is based on human visual characteristics, Intermediate frequency
coefficient through DWT is used to embed watermark, and meaningful binary image is
used as watermark. According to different watermark images, the intermediate
frequency coefficient was changed twice to embed watermark in order enhance
robustness.
3.Combining double random phase modulation encryption holographic technology
with CIELab color space, DWT with DCT, an encryption holographic watermarking
algorithm was proposed. Double random phase modulation encryption holographic
technology can ensure the security and blind extraction.
4. On the basis of Fourier encryption holographic technology and digital
watermarking, DWT, a Fourier encryption holographic algorithm based on DWT was