This paper addresses the problem of content-based synchronization
for robust watermarking. Synchronization is a process of extracting the location
to embed and detect the signature, copyright information, so that it is crucial for
the robustness of the watermarking system. In this paper, we will review representative
content-based approaches and propose a new synchronization method
based on the scale invariant feature transform. In content-based synchronization
approaches, it is important to extract robust features even with image distortions
and we suspect that the consideration of local image characteristics will be
helpful. The scale invariant feature transform regards these characteristics and
is invariant to noise, spatial filtering, geometric distortions, and illumination
changes of the image. Through experiments, we will compare the proposed
method with representative content-based approaches and show the appropriateness
for robust watermarking.