Robust image watermark with wavelet transform and spread spectrum techniques

The wavelet packet transform and spread spectrum techniques are used to achieve image watermark processing. In the first stage of the proposed method, the original image is converted to the frequency domain with the wavelet packet transform. The watermark is then embedded to the image by adding the data into the significant coefficients in the wavelet packet domain. With this scheme, the watermark data is not easily distorted when processing such as compression and translation are performed. In addition, the spread spectrum technique is adopted to increase the security of the watermark. The pseudo-noise sequence is utilized to decide which subband of the wavelet packet transform is performed such that only the authorized people who have the pattern of the pseudo-noise sequence can retrieve the watermark data. From the simulation results, the approach is shown to have a good performance and is robust to image processing and attack.