Digital watermarking schemes have been discussed to solve the problem associated with copyright enforcement. As a digital watermarking, we proposed a method using inter-block correlation of DCT coefficients. It has the features that the embedded watermark can be extracted without the original image nor the parameters used in embedding process and that the amount of modification, the strength of embedded watermark, depends on the local feature of an image. This feature makes it difficult for pirate to predict the position in which the watermark signal is embedded. In this paper, we propose a method which can embed/extract watermark with high speed by utilizing this watermarking method for JPEG file format.