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USING INVISIBLE WATERMARKS TO PROTECT VISIBLY WATERMARKED IMAGES. C.M.Chen. Outline. Introduction Framework Robust Invisible Watermarking Algorithm Experimental Results Future Work. Introduction. - PowerPoint PPT Presentation
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Outline
Introduction Framework Robust Invisible Watermarking Algorithm Experimental Results Future Work
Introduction
Several visible watermarking techniques have been proposed in the literature, and meanwhile, some problems with visible watermarks are also under investigation
1. watermark removal
2. unauthorized insertion
Introduction
In this paper, we propose using an invisible watermark in visibly watermarked images to overcome these problems
Visible watermarks are useful for protecting online images because they discourage unauthorized copying
Several visible watermarking techniques have been proposed in the literature
Introduction
Generally, visible watermarking requires that each watermark should be easily visible, unobtrusive, and hard to remove
Although we can use a number of methods to make the visible watermark difficult to remove, we have to admit that removal is not impossible
Introduction
some researchers have attempted to remove the embedded watermark by using image inpainting techniques
a visible watermark bearing a certain logo does not constitute a proof of ownership
some one can insert the logo of others within an image and claim that the resulting image comes from them
Introduction
the first is that a visible watermark must be difficult to remove
the second is that it must be able to withstand the impersonator problem
Most efforts in the literature focus on the first problem
However, to the best of our knowledge, there are few papers available for the second problem
Introduction
Mohanty et al. presented a dual watermarking technique which attempts to establish the owner’s right to the image and detect the intentional and unintentional tampering of the image
They claimed that if anybody tries to tamper the visible watermark intentionally, they can know the extent of tampering with the help of invisible watermark detection algorithm
Introduction
However, they obviously did not distinguish between the tampering of the visibly watermarked image and that of the embedded visible watermark
it is unable to tell whether those changes are targeted at the embedded visible watermark or the visibly watermarked image
Introduction
Wong and Memon used an invisible authentication watermark to ensure the identity of a visibly watermarked image
Any modification to the visible watermark would be reflected in a corresponding error in the fragile watermark
However, their scheme is too sensitive to be used in most practical applications
Some apparent disadvantages of using fragile watermarks for this purpose1. Common image processing such as compre
ssion, filtering, noise addition or geometric distortion can not hinder the embedded visible watermark from indicating ownership, but they can destroy the fragile watermark easily
Some apparent disadvantages of using fragile watermarks for this purpose2. When the owner’s visible watermark is
visually removed or tampered, or replaced by another unauthorized visible watermark, one can not identify the right owner to the image with the fragile watermarking scheme
Motivation
We need an invisible watermark that can enhance ownership protection of the visibly watermarked image
Ownership assertion watermarks are typically robust
So we need a robust instead of fragile invisible watermarking scheme in the dual watermarking system
The properties and associated requirements of such robust watermarks1)The watermark should be invisible and has n
o apparent interference with the visibly watermarked image
2)The watermark is desirously extracted without resorting to the visibly watermarked image
3)The watermark must be difficult to remove and can resist non-malicious changes such as image compression and malicious attacks such as image inpainting/replacement
The properties and associated requirements of such robust watermarks Visibly watermarked images are usually
compressed for online use So malicious attacks may be targeted at the
compressed-decompressed versions of images
The most challenge to such a watermarking technique is to make the invisible watermark robust against operations like compression and image inpainting
Robust invisible watermarking algorithm Since content-preserving image processing s
uch as compression has low-pass nature, it is reasonable to choose the low-pass component for watermark embedding
In this paper, we propose to embed the invisible watermark in the low-pass subband of a three-level wavelet decomposition image
Robust invisible watermarking algorithm Image inpainting/replacement will affect all th
e frequency components of any watermarking scheme based on a global transform, whereas the DWT-based scheme produces watermarks with local spatial support
The selection of three-level decomposition is to make the number of low-pass coefficients large enough for watermark embedding
Robust invisible watermarking algorithm
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Constructing invisible watermarks In this paper, we choose the watermark in the
form of the binary image of the embedded visible watermark so that the extracted logo can indicate the ownership without additional computing
To increase the security of the invisible watermark, the invisible watermark image is shuffled with some techniques like chaotic mapping before embedding (Here we use the Arnold’s cat map to transform the binary logo)
Constructing invisible watermarks After transformation, a binary block which foll
ows uniform distribution and has the same size as the binary logo is EX-ORed with the binary logo to create the encrypted watermark
The seed of the pseudo-random number generator is used as the private key
Constructing invisible watermarks In watermark detection, without the private ke
y, one can only obtain a meaningless binary sequence. However, legal users can recreate the binary logo by EX-ORing the extracted block with the pseudo-random block generated with the private key
Post-processing extracted invisible watermarks From experiments we notice that image oper
ations like compression and inpainting/replacement have different effects on the extracted binary image
The former produces random noise-like pixels across the entire extracted image whereas the latter only ruins parts of the image
Post-processing extracted invisible watermarks This is because compression could alter valu
es of some low-pass coefficients and thus cause parts of embedded information bits not to be extracted correctly
With higher compression ratio, more noise-like pixels would appear
Post-processing extracted invisible watermarks On the other side, inpainting/replacement, wh
ich is often a kind of spatial operation, only causes information bits embedded in targeted areas to be lost
To remove noise-like pixels resulting from compression, we use a median filter to post-process the extracted binary image
After such a non-linear filtering, most isolated noise-like pixels can be removed
Future research
Future efforts will focus on how to enhance robustness of the embedded invisible watermark, for example, to make the watermark against geometrical attacks which challenge all existing invisible watermarks
How to embed more watermark information is another major concern.
The research on dual watermarking system is very significant for the practical application of visible watermarks