An optimized scheme for watermarking based on zerotrees is proposed in this paper. Digital watermarking is an effective means for protecting copyrights with three of the most fundamental requirements: watermark imperceptibility, watermark robustness, and watermark capacity. Conventional techniques in the literature mainly perform watermark embedding and extraction processes in the transform domain, including the discrete Fourier transform, discrete cosine transform, and discrete wavelet transform domains. The three watermarking requirements above are in conflict with each other; therefore, finding a way to obtain a trade-off among them is the major purpose of this paper. We first perform watermarking in the wavelet domain. Next, we properly select zerotrees in a wavelet transform with the genetic algorithm. Our simulation results not only demonstrate better performances of the watermarked images after optimization, but also reveal the robustness of the extracted watermarks under common attacks.