Abstract
In this thesis, we use 1024-bits RSA cryptography to protect the trade messages. We also use digital signature to prevent a buyer from unauthorized copies and to prevent a seller from forged unauthorized copies. We encode the signature with bar-code and embed the bar-code image into the original image. As long as the similarity of watermark extracts from the damaged image over a threshold, the signature can be fully recovered. It is a new idea to bring the bar-code concept into the watermark system. The general method of robust watermark that people would utilize is to embed a meaningful logo into an image and correct the damaged watermark with error correcting code (ECC). Our simulation shows that the proposed algorithm gets much better results than that with ECC.