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In this paper, a robust digital watermarking algorithm using wavelet transform is proposed. In order to equally embed the watermark to the whole image, the coefficients of all subbands including LL subband are utilized. To select perceptually significant coefficients for each subband, a level-adaptive thresholding scheme is used. The watermark is embedded to the selected coefficients, using different scale factors depending on the level of decomposition. In the detection process, the vector projection method is used. The performance of the proposed algorithm compared with other transform-domain watermarking methods has been analyzed, using various rest images. The experimental results have shown that the proposed watermark is invisible to human eyes and very robust to various attacks, such as image compression, image filtering, geometric transformations and noises.