Originated from the extensive applications of remotely sensed imagery, Earth observation missions have drawn increasing attention from the scientific and industrial communities. Mostly available in digital forms, remote sensing imagery is easily distributed for unauthorized use, and its copyright protection is becoming nontrivial. For the watermarking of pan-sharpened IKONOS and QuickBird imagery, in this work, a fast and robust approach is proposed for preventing illegal use and malicious modification. Directly in RGB color space, multiple watermarks are embedded into the saturation component by exploiting the properties of intensity-hue-saturation color space and the discrete cosine transform. To resist general cropping, rotation, and resizing attacks on remote sensing imagery, a real system, named StarMarker, was implemented and tested. Experimental results show that this scheme can successfully make the multiple watermarks perceptually invisible and defeat composite attacks of cropping with rotation, high-pass filtering, saturation and hue adjustment, and JPEG compression. The merits of the proposed watermarking system not only provide promising performance but also achieve the purpose of copyright protection.