Phase watermarking of digital images

Abstract

A watermark is an invisible mark placed on an image that can be detected when the image is compared with the original. The mark is designed to identify both the source of an image as well as its intended recipient. The mark should be tolerant to reasonable quality lossy compression of the image using transform coding or vector quantization. Standard image processing operations such as low pass filtering, cropping, translation and rescaling should not remove the mark. Spread spectrum communication techniques and matrix transformations can be used together to design watermarks that are robust to tampering and are visually imperceptible. This paper discusses techniques for embedding such marks in grey scale digital images. It also proposes a novel phase based method of conveying the watermark information. In addition, the use of optimal detectors for watermark identification is also proposed

Rotation, scale and translation invariant spread spectrum digital image watermarking

“…It was also found that the watermark survived lossy image compression using JPEG at normal settings (75% quality factor). Other methods exist that tolerate JPEG compression down to 5% quality factor [7,6,16,15]; work is underway to combine these with this approach. In addition, the mark is also reasonably resistant to cropping and could be recovered from a segment approximately 50% of the size of the original image.…”

“…Many of the current techniques for embedding marks in digital images have been inspired by methods of image coding and compression. Information has been embedded using the Discrete Cosine Transform (DCT) [16,34,5,6] Discrete Fourier Transform magnitude and phase [15], Wavelets [16], Linear Predictive Coding [13] and Fractals [9,22]. The key to making watermarks robust has been the recognition that in order for a watermark to be robust it must be embedded in the perceptually signi cant components of the image [16,5,6].…”

Survey on Classification of Different Video Watermarking Techniques

“…Ruanaidh et. al projected watermarking in the frequency domain [26] through the amendment of the phase. The phase of a preferred coefficient of an N1×N2, DFT is adopted to insert a bit by adding a small 'δ'.…”

Robustness and security of digital watermarks

“…If a transformed representation is used, it may be applied to the entire data (the whole image), or on a block-by-block basis. For images, watermarks have been applied to pixels [2], Fourier components [24], whole-image and block-based discrete cosine components [8,23,39], wavelet components [23], and Fourier-Mellin components [25,13]. One use of a transformed representation is to make the components of the data more independent; pixels in an image, for example, are highly correlated locally, which is not true of discrete cosine components.…”