Robust LSB Watermarking Optimized for Local Structural Similarity

Growth of the Internet and networked multimedia systems has emphasized the need for copyright protection of the media. Media can be images, audio clips, videos and etc. Digital watermarking is today extensively used for many applications such as authentication of ownership or identification of illegal copies. Digital watermark is an invisible or maybe visible structure added to the original media (known as asset). Images are considered as communication channels when they are subject to a watermark embedding procedure so in the case of embedding a digital watermark in an image, the capacity of the channel should be considered. There is a trade-off between imperceptibility, robustness and capacity for embedding a watermark in an asset. In the case of image watermarks, it is reasonable that the watermarking algorithm should depend on the content and structure of the image. Conventionally, mean squared error (MSE) has been used as a common distortion measure to assess the quality of the images. Newly developed quality metrics proposed some distortion measures that are based on human visual system (HVS). These metrics show that MSE is not based on HVS and has a lack of accuracy when dealing with perceptually important signals such as images and videos. SSIM or structural similarity is a state of the art HVS based image quality criterion that has recently been of much interest. In this paper we propose a robust least significant bit (LSB) watermarking scheme which is optimized for structural similarity. The watermark is embedded into a host image through an adaptive algorithm. Embedding will continue in each block of the host image until a certain level of threshold in the structural similarity is met. Various attacks examined on the embedding approach and simulation results revealed the fact that the watermarked sequence can be extracted with an acceptable accuracy after all attacks. In comparison to the original algorithm, the proposed method increases the capacity while the imperceptibility and robustness remain fix.