2 research outputs found
Optimisation of Tamper Localisation and Recovery Watermarking Techniques
Digital watermarking has found many applications in many fields, such as:
copyright tracking, media authentication, tamper localisation and recovery,
hardware control, and data hiding. The idea of digital watermarking is to embed
arbitrary data inside a multimedia cover without affecting the perceptibility of the
multimedia cover itself. The main advantage of using digital watermarking over
other techniques, such as signature based techniques, is that the watermark is
embedded into the multimedia cover itself and will not be removed even with the
format change.
Image watermarking techniques are categorised according to their robustness
against modification into: fragile, semi-fragile, and robust watermarking. In fragile
watermarking any change to the image will affect the watermark, this makes fragile
watermarking very useful in image authentication applications, as in medical and
forensic fields, where any tampering of the image is: detected, localised, and
possibly recovered. Fragile watermarking techniques are also characterised by a
higher capacity when compared to semi-fragile and robust watermarking. Semifragile
watermarking techniques resist some modifications, such as lossy
compression and low pass filtering. Semi-fragile watermarking can be used in
authentication and copyright validation applications whenever the amount of
embedded information is small and the expected modifications are not severe.
Robust watermarking techniques are supposed to withstand more severe
modifications, such as rotation and geometrical bending. Robust watermarking is
used in copyright validation applications, where copyright information in the image
must remains accessible even after severe modification.
This research focuses on the application of image watermarking in tamper
localisation and recovery and it aims to provide optimisation for some of its
aspects. The optimisation aims to produce watermarking techniques that enhance
one or more of the following aspects: consuming less payload, having better
recovery quality, recovering larger tampered area, requiring less calculations, and
being robust against the different counterfeiting attacks. Through the survey of the main existing techniques, it was found that most of them
are using two separate sets of data for the localisation and the recovery of the
tampered area, which is considered as a redundancy. The main focus in this
research is to investigate employing image filtering techniques in order to use only
one set of data for both purposes, leading to a reduced redundancy in the
watermark embedding and enhanced capacity. Four tamper localisation and
recovery techniques were proposed, three of them use one set of data for
localisation and recovery while the fourth one is designed to be optimised and
gives a better performance even though it uses separate sets of data for
localisation and recovery.
The four techniques were analysed and compared to two recent techniques in the
literature. The performance of the proposed techniques vary from one technique to
another. The fourth technique shows the best results regarding recovery quality
and Probability of False Acceptance (PFA) when compared to the other proposed
techniques and the two techniques in the literature, also, all proposed techniques
show better recovery quality when compared to the two techniques in the
literature
A robust region-adaptive digital image watermarking system
Digital image watermarking techniques have drawn the attention of researchers and practitioners as a means of protecting copyright in digital images. The technique involves a subset of information-hiding technologies, which work by embedding information into a host image without perceptually altering the appearance of the host image. Despite progress in digital image watermarking technology, the main objectives of the majority of research in this area remain improvements in the imperceptibility and robustness of the watermark to attacks. Watermark attacks are often deliberately applied to a watermarked image in order to remove or destroy any watermark signals in the host data. The purpose of the attack is. aimed at disabling the copyright protection system offered by watermarking technology. Our research in the area of watermark attacks found a number of different types, which can be classified into a number of categories including removal attacks, geometry attacks, cryptographic attacks and protocol attacks. Our research also found that both pixel domain and transform domain watermarking techniques share similar levels of sensitivity to these attacks. The experiment conducted to analyse the effects of different attacks on watermarked data provided us with the conclusion that each attack affects the high and low frequency part of the watermarked image spectrum differently. Furthermore, the findings also showed that the effects of an attack can be alleviated by using a watermark image with a similar frequency spectrum to that of the host image. The results of this experiment led us to a hypothesis that would be proven by applying a watermark embedding technique which takes into account all of the above phenomena. We call this technique 'region-adaptive watermarking'. Region-adaptive watermarking is a novel embedding technique where the watermark data is embedded in different regions of the host image. The embedding algorithms use discrete wavelet transforms and a combination of discrete wavelet transforms and singular value decomposition, respectively. This technique is derived from the earlier hypothesis that the robustness of a watermarking process can be improved by using watermark data in the frequency spectrum that are not too dissimilar to that of the host data. To facilitate this, the technique utilises dual watermarking technologies and embeds parts of the watermark images into selected regions of the host image. Our experiment shows that our technique improves the robustness of the watermark data to image processing and geometric attacks, thus validating the earlier hypothesis. In addition to improving the robustness of the watermark to attacks, we can also show a novel use for the region-adaptive watermarking technique as a means of detecting whether certain types of attack have occurred. This is a unique feature of our watermarking algorithm, which separates it from other state-of-the-art techniques. The watermark detection process uses coefficients derived from the region-adaptive watermarking algorithm in a linear classifier. The experiment conducted to validate this feature shows that, on average, 94.5% of all watermark attacks can be correctly detected and identified