In practical use, objects in still images and videos are easy to misappropriate with handy image-processing tools and need to be protected. However, the few proposals for object watermarking suffer from resynchronization problems. In this study, we develop an object-based watermarking method based on efficient segmentation using lines parallel and perpendicular to two principal axes in the spatial domain. A patchlike scheme is designed to embed and extract invisible watermarks. In contrast with the previous object-based watermarking schemes, extra information for resynchronization is not required to be stored in our method. Experimental results show the robustness of the proposed method against many kinds of geometrical attacks.