Image watermarking with feature point based synchronization robust to print-scan attack

In this paper we propose a content based multibit watermarking method robust to print-scan attack. A method to extract feature points, robust in terms of watermarking, is proposed. The location of the watermark is tied to a coordinate system defined by robust feature points. A message sequence is mapped to a directional angle of periodic patterns, which are scattered and embedded into triangles in permuted locations. In watermark extraction, an interplay between feature extraction and watermarking ensures reliability and a multibit message can be decoded blindly from the locations pointed by the key. By detecting the alignment of the autocorrelations peaks and using a coding table, a multibit message can be extracted. Experiments show that the method provides robust and blind extraction of watermark information after a print-scan attack and a set of compound attacks.