Abstract
A watermarking scheme is presented in which the characteristics of both spatial and frequency techniques are combined to achieve robustness against image processing and geometric transformations. The proposed approach consists of three basic steps: estimation of the just noticeable image distortion, watermark embedding by adaptive spreading of the watermark signal in the frequency domain, and extraction of relevant information relating to the spatial distribution of pixels in the original image. The just noticeable image distortion is used to insert a pseudo-random signal such that its amplitude is maintained below the distortion sensitivity of the pixel into which it is embedded. Embedding the watermark in the frequency domain guarantees robustness against compression and other common image processing transformations. In the spatial domain most salient image points are characterized using the set of Hilbert first-order differential invariants. This information is used to detect geometrical attacks in a frequency-domain watermarked image and to resynchronize the attacked image. The presented schema has been evaluated experimentally. The obtained results show that the technique is resilient to most common attacks including rotation, translation, and scaling.
Highlights
Conventional analog media distribution systems have an inherent built-in defense against copying, alteration, and fraud
We propose to combine frequency and spatial domain watermarking strategies into a new model in which the different robustness properties of both schemes are consistently exploited
First-order invariant image primitives have been combined with a spread spectrum approach to produce a novel watermarking scheme
Summary
Conventional analog media distribution systems have an inherent built-in defense against copying, alteration, and fraud. The major challenge is to find a strategy that satisfies the conflicting objectives of performing image changes that are imperceptible for the human eye and being extremely robust against detection or removal either accidentally or intentionally. These two objectives are conflicting in nature because it is not possible to simultaneously maximize robustness and imperceptibility. On the other hand, keeping imperceptibility means keeping the embed amount of information minimal and very susceptible to removal or detection
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