In this thesis, we proposed two frequency-based watermarking algorithms. One is DCT-based method. Embedding watermark in the multi-areas and multi- frequency bands to ensure we can get a less distorted watermark sequence under unintentional circumstance. The other is DWT-based method. The parent-children relationship and the feature of bit-plane coding in the EZW algorithm are exploited to embed watermark. It makes that we can know the watermark exist or not in the progressive transmission system. The experimental results show that the proposed methods both can resist unintentional attacks. The DWT-based method also has a better progressive detection capability.