Digital watermark for document electronic seal system based on DCT technology

According to the characteristics of the electronic seal and the special security requirement, a watermarking scheme for electronic seal based on the discrete cosine transform is proposed. The theory of digital watermark based on DWT for electronic seal is discussed. In the process of embedding the watermark image is processed by Arnold transformation and the original image is divided into some blocks which are transformed into coefficients in the DCT domain. The average value of coefficients selected from the same location in DCT blocks is calculated according to the Arnold transformed watermark value. The algorithm of how to embed and extract the watermark is shown in the paper. The experimental results demonstrate the efficiency of the proposed scheme, which fulfills the strict requirements of electronic seal and which is practicality perfect by means of good balance between transparency and robustness.