Abstract: An adaptive digital watermarking algorithm based on discrete Fourier transform(DFT) is proposed to protect the copyright of digital raster maps.This algorithm can utilize the human visual system(HVS) and the blocking DFT to determine adaptively the texture region where the watermarking information can be hidden.And the watermarking information is embedded to the middle frequency coefficient of the Fourier transform domain of the texture region.The algorithms with different size blocking(blocks) have different robustness.This problem is discussed,and these algorithms are analyzed with different size blocking,such as the 2×2 blocking,the 4×4 blocking and the 8×8 blocking.Experimental results show that the algorithm with 2×2 blocking not only has the good transparency,but also has the good robustness to the image intensity attack such as cropping,JPEG compression,noise adding,image enhancement,and so on.The algorithm with 2×2 blocking performs better than the algorithms with 4×4 blocking and the 8×8 blocking.