Disclosed is a method for embedding and extracting a spatial domain blind watermark using a sample expansion. The sample expansion method using a sample expansion coefficient is introduced to basically improve a common disadvantage of the conventional watermarking method based on the patchwork method, for instance, the watermark is not robust against a compression attack such as JPEG. By applying the sample expansion to a sample group, the embedded watermark comes to contain a low frequency component more larger than ever, so that radio frequency component decreases as much. Thus, although the radio frequency component of the watermark is damaged by the image compression such as JPEG, it is possible to relatively reduce the damage of the watermark. Also, an adaptive watermark embedding method can be considered such that the embedded watermark value is proportional to an average value of the pixel. In order to overcome non-robustness that is a common disadvantage of the conventional methods based on the conventional patchwork method or the conventional modified patchwork method, not a single pixel but sample-expanded pixel is chosen, and there is proposed a spatial domain blind watermarking method using a watermark value that is proportional to an average value of pixel every tile.