We propose a digital watermarking algorithm based on the Slant transform for the copyright protection of complex textured images. A lot of images in practical applications, such as remote sensing and medical archiving, contain complex textures. With more AC energies concentrating in the high frequency components, images with complex textures usually suffer more from common image processing operations than smooth images do. Therefore, watermarking robustness is more an issue for textured images though it is commonly recognized that highly textured images provide more capacity for data hiding without introducing too much degradation to the visual quality of original images. Experimental results showed that our Slant transform watermarking provides significant advantage for watermarking insertion and retrieval for images with complex textures such as satellite images. 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 and Checkmark attacks.