In this paper, we propose a digital watermarking algorithm based on the Slant transform for the copyright protection of satellite images. Designed to match basis vectors to areas of constant luminance slope, the Slant transform is good for compact energy in "smooth" images. However, our earlier research work suggests that in terms of watermarking, it works better for textured images, for the energy spread becomes a significant advantage in watermarking and offers a good spread of middle to higher frequencies with significant energies for robust information hiding. This has brought us to consider protecting the copyright of digital satellite images using Slant transform watermarking, which is commonly highly textured. An analytical comparative study on the performance of the Slant transform adapting our earlier watermarking schemes for fast Hadamard transform will be performed based on its robustness against various Stirmark attacks.