In recent years, image watermarking has attracted much attention as an effective copyright protection technique for digital
images. By hiding watermark information in digital images, image watermarks can provide copyright protection. Usually,
digital watermarking has two performance measures: imperceptibility and robustness. However, embedding watermarks
into digital images can degrade the images’ visual quality, and it is desirable for the degradation to not be easily noticed.
Therefore, imperceptibility denotes the idea that an embedded watermark should be invisible to the human visual system
(HVS). During use and distribution, watermarked images may suffer from distortions caused by common signal processing
operations, lossy image compression, and other attacks; thus, watermarks should be robustly resistant to image distortions.
Therefore, robustness means that watermarks should be effectively detected after undergoing most common signal processing
operations or attacks. In the past ten years, many image watermarking methods have been proposed.