A novel robust watermarking scheme based on image connectivity is proposed. In the scheme, the connected objects are obtained according to selected connectivity pattern, and the gravity centers are calculated in several bigger objects as the reference points for watermark embedding. Based on these reference points and the center of the whole image, several sectors are formed, and the same version of watermarks is embedded into these sectors and their opposites. Thanks to the very stable gravity center of the connected objects, watermark detection is synchronized successfully. Simulation results show that the watermark can survive under both local and global geometrical distortions.