Signal Processing 88 (2008) 539–557 An interpolation-based watermarking scheme V. Martin à , M. Chabert, B. Lacaze ENSEEIHT/IRIT, National Polytechnic Institute of Toulouse, 2 Rue Camichel, BP 7122, 31071 Toulouse Cedex 7, France Received 5 April 2007; received in revised form 2 August 2007; accepted 28 August 2007 Available online 4 September 2007 Abstract Interpolation techniques are often designed to provide a good perceptual quality from known sample values. However, interpolation is essentially considered as a source of decoding errors for watermarking schemes. Conversely, this paper proposes an informed watermarking scheme based on interpolation. This scheme takes advantage of interpolation to generate imperceptible marks in the spatial domain. It can be related to random binning schemes with particular codebook and decoding rule. Theoretical performances are derived and informed embedding strategies are proposed. Two particular implementations based on bilinear and spline interpolation are then applied to image watermarking. The good robustness of these schemes to noise and valumetric attacks is confirmed by simulations. Finally, an attack is specifically designed to check the algorithm security. r 2007 Elsevier B.V. All rights reserved. Keywords: Digital watermarking; Interpolation; Informed embedding 1. Introduction 1.1. Digital watermarking Digital watermarking consists of embedding data at the content-level of digital media under con- straints on imperceptibility, security and robustness to attacks. Its applications range from digital rights management to integrity protection. This paper considers scenarios where document-dependent watermarks can be embedded. This includes the copyright protection application. The host docu- ment is not used at the detection. In direct sequence (DS) spread spectrum water- marking [1], the additive mark is the message modulated by a pseudo-noise. The message can be decoded by correlation with this pseudo-noise. Classical spread spectrum methods are subject to host interference. Extensions provide improved performance thanks to Wiener prefiltering before decoding (DS þ W) or optimal decoding for a given host statistical model [2]. Informed watermarking provides better performance when the host signal is known to the embedder [3]. In informed coding, a watermark template is directly generated from the host document. It can be combined with informed embedding, which uses knowledge upon both the host and the decoding technique. Specific strategies are designed to improve imperceptibility, robustness or detection receiver performance. For instance, linear improved spread spectrum (LISS) [4] is a modulation technique derived from DS. It removes ARTICLE IN PRESS www.elsevier.com/locate/sigpro 0165-1684/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.sigpro.2007.08.016 à Corresponding author. IRIT-ENSEEIHT, 2 rue Charles Camichel, B.P. 7122, 31000 Toulouse, France. Tel.: +33 561588072; fax: +33 561588306. E-mail addresses: vincent.martin@enseeiht.fr (V. Martin), bernard.lacaze@enseeiht.fr (B. Lacaze).