Abstract
In recent years, digital watermark is important for academic research and industry application. It can be applied in multimedia data such as digital music, images and videos etc. Watermarking technology adds a watermark,visible or invisible,on the these signals for copyright protection.In order that to ensure watermark’s robustness, it will effect to the image quality.On the other hand, if you want to have good image quality, it will affect the watermark’s validity. It is a trade-off between watermark robustness and image quality. There are two domain researches on watermark technology.One is the spatial domain technique, and the other is frequency domainTechnique. Recently, wavelet transform has been adopted in JPEG 2000 and MPEG 4. It is very important for image coding. Encryption algorithm is one of the cipher security. In1977,American government released the DES encryption algorithm in public. However, the 56 bits key’s DES algorithm is almost over. Therefore, in 1997, American government asked for developing the advanced encryption algorithm fothe next generation.