In this paper, comparative analysis on the characteristics of the Pseudo Random Sequence(PRS) and the Normal Random Sequence(NRS) which are used as a watermark for copyright protection and authentication about digital media in the conventional digital watermarking systems. From the analysis, it is found that in case of the NRS, the detection of the watermark might be difficult by many crosscorrelation peak values from other NRS codes because of the non-uniform distribution of 1 and 0 in those codes. However, in case of the PRS, since it has the uniform distribution of the random number in the generated codes, there exists very few crosscorrelation peaks. So the PRS is analyzed to be more robust against possible attacks such as JPEG image compression and Gaussian noise compared with the case of the NRS. Finally, in this paper, simulation results on the robustness of the PRS and NRS against some attacks such as JPEG compression, Gaussian noise are also suggested.