For copyright protection, the robustness of a watermarking scheme against various attacks is an essential requirement. Many proposed robust watermarking schemes may achieve good robustness but sacrifice the good quality of the watermarked image. This paper, therefore, proposes a transparent robust watermarking scheme, which embeds the watermark (or the secret information) adaptively in the Discrete-Cosine Transform (DCT) domain. The proposed scheme is blind as the original image is not needed, and only a key containing the watermark locations and the scaling factors is required for watermark extraction. This adaptive replacement embedding technique can guarantee in preserving the good visual quality of a watermarked image. Comparing with other existing DCT-domain watermarking methods, the proposed watermarking method can achieve higher robustness performance, while retaining better quality of the watermarked image in terms of PSNR.