23 research outputs found

    Digital watermark technology in security applications

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    With the rising emphasis on security and the number of fraud related crimes around the world, authorities are looking for new technologies to tighten security of identity. Among many modern electronic technologies, digital watermarking has unique advantages to enhance the document authenticity. At the current status of the development, digital watermarking technologies are not as matured as other competing technologies to support identity authentication systems. This work presents improvements in performance of two classes of digital watermarking techniques and investigates the issue of watermark synchronisation. Optimal performance can be obtained if the spreading sequences are designed to be orthogonal to the cover vector. In this thesis, two classes of orthogonalisation methods that generate binary sequences quasi-orthogonal to the cover vector are presented. One method, namely "Sorting and Cancelling" generates sequences that have a high level of orthogonality to the cover vector. The Hadamard Matrix based orthogonalisation method, namely "Hadamard Matrix Search" is able to realise overlapped embedding, thus the watermarking capacity and image fidelity can be improved compared to using short watermark sequences. The results are compared with traditional pseudo-randomly generated binary sequences. The advantages of both classes of orthogonalisation inethods are significant. Another watermarking method that is introduced in the thesis is based on writing-on-dirty-paper theory. The method is presented with biorthogonal codes that have the best robustness. The advantage and trade-offs of using biorthogonal codes with this watermark coding methods are analysed comprehensively. The comparisons between orthogonal and non-orthogonal codes that are used in this watermarking method are also made. It is found that fidelity and robustness are contradictory and it is not possible to optimise them simultaneously. Comparisons are also made between all proposed methods. The comparisons are focused on three major performance criteria, fidelity, capacity and robustness. aom two different viewpoints, conclusions are not the same. For fidelity-centric viewpoint, the dirty-paper coding methods using biorthogonal codes has very strong advantage to preserve image fidelity and the advantage of capacity performance is also significant. However, from the power ratio point of view, the orthogonalisation methods demonstrate significant advantage on capacity and robustness. The conclusions are contradictory but together, they summarise the performance generated by different design considerations. The synchronisation of watermark is firstly provided by high contrast frames around the watermarked image. The edge detection filters are used to detect the high contrast borders of the captured image. By scanning the pixels from the border to the centre, the locations of detected edges are stored. The optimal linear regression algorithm is used to estimate the watermarked image frames. Estimation of the regression function provides rotation angle as the slope of the rotated frames. The scaling is corrected by re-sampling the upright image to the original size. A theoretically studied method that is able to synchronise captured image to sub-pixel level accuracy is also presented. By using invariant transforms and the "symmetric phase only matched filter" the captured image can be corrected accurately to original geometric size. The method uses repeating watermarks to form an array in the spatial domain of the watermarked image and the the array that the locations of its elements can reveal information of rotation, translation and scaling with two filtering processes

    Digital 3D documentation of cultural heritage sites based on terrestrial laser scanning

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    Deniable Storage Encryption for Mobile Devices

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    Smartphones, and other mobile computing devices, are being widely adopted globally as the de-facto personal computing platform. Given the amount of sensitive information accumulated by these devices, there are serious privacy and security implications for both personal use and enterprise deployment. Confidentiality of data-at-rest can be effectively preserved through storage encryption. All major mobile OSes now incorporate some form of storage encryption. In certain situations, this is inadequate, as users may be coerced into disclosing their decryption keys. In this case, the data must be hidden so that its very existence can be denied. Steganographic techniques and deniable encryption algorithms have been devised to address this specific problem. This dissertation explores the feasibility and efficacy of deniable storage encryption for mobile devices. A feature that allows the user to feign compliance with a coercive adversary, by decrypting plausible and innocuous decoy data, while maintaining the secrecy of their sensitive or contentious hidden data. A deniable storage encryption system, Mobiflage, was designed and implemented for the Android OS, the first such application for mobile devices. Current mobile encryption mechanisms all rely, in some way, on a user secret. Users notoriously choose weak passwords that are easily guessed/cracked. This thesis offers a new password scheme for use with storage encryption. The goal is to create passwords that are suitably strong for protection of encryption keys, easier to input on mobile devices, and build on memorability research in cognitive psychology for a better user experience than current password guidelines

    Algorithms for propagation-aware underwater ranging and localization

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    Mención Internacional en el título de doctorWhile oceans occupy most of our planet, their exploration and conservation are one of the crucial research problems of modern time. Underwater localization stands among the key issues on the way to the proper inspection and monitoring of this significant part of our world. In this thesis, we investigate and tackle different challenges related to underwater ranging and localization. In particular, we focus on algorithms that consider underwater acoustic channel properties. This group of algorithms utilizes additional information about the environment and its impact on acoustic signal propagation, in order to improve the accuracy of location estimates, or to achieve a reduced complexity, or a reduced amount of resources (e.g., anchor nodes) compared to traditional algorithms. First, we tackle the problem of passive range estimation using the differences in the times of arrival of multipath replicas of a transmitted acoustic signal. This is a costand energy- effective algorithm that can be used for the localization of autonomous underwater vehicles (AUVs), and utilizes information about signal propagation. We study the accuracy of this method in the simplified case of constant sound speed profile (SSP) and compare it to a more realistic case with various non-constant SSP. We also propose an auxiliary quantity called effective sound speed. This quantity, when modeling acoustic propagation via ray models, takes into account the difference between rectilinear and non-rectilinear sound ray paths. According to our evaluation, this offers improved range estimation results with respect to standard algorithms that consider the actual value of the speed of sound. We then propose an algorithm suitable for the non-invasive tracking of AUVs or vocalizing marine animals, using only a single receiver. This algorithm evaluates the underwater acoustic channel impulse response differences induced by a diverse sea bottom profile, and proposes a computationally- and energy-efficient solution for passive localization. Finally, we propose another algorithm to solve the issue of 3D acoustic localization and tracking of marine fauna. To reach the expected degree of accuracy, more sensors are often required than are available in typical commercial off-the-shelf (COTS) phased arrays found, e.g., in ultra short baseline (USBL) systems. Direct combination of multiple COTS arrays may be constrained by array body elements, and lead to breaking the optimal array element spacing, or the desired array layout. Thus, the application of state-of-the-art direction of arrival (DoA) estimation algorithms may not be possible. We propose a solution for passive 3D localization and tracking using a wideband acoustic array of arbitrary shape, and validate the algorithm in multiple experiments, involving both active and passive targets.Part of the research in this thesis has been supported by the EU H2020 program under project SYMBIOSIS (G.A. no. 773753).This work has been supported by IMDEA Networks InstitutePrograma de Doctorado en Ingeniería Telemática por la Universidad Carlos III de MadridPresidente: Paul Daniel Mitchell.- Secretario: Antonio Fernández Anta.- Vocal: Santiago Zazo Bell

    Designable Visual Markers for Mobile Human-Computer Interaction

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    Visual markers are graphic symbols designed to be easily recognised by machines. They are traditionally used to track goods, but there is increasing interest in their application to mobile human-computer interaction (HCI). By scanning a visual marker through a camera phone, users can retrieve localised information and access mobile services. In particular the dissertation examines the application of visual markers to physical tagging: practices of association of digital information with physical items. One missed opportunity in current visual marker systems is that the markers themselves cannot be visually designed; they are not expressive to humans, and thus fail to convey information before being scanned. To address this limitation, this dissertation introduces the idea of designable markers, visual markers that are both machine-readable and visually communicative to humans, and presents an investigation of the ways in which they can support mobile human-computer interaction. The application of designable visual markers to the creation of mobile interfaces is explored through a variety of methods: through formal usability experiments, through the creation and analysis of example designs, as well as through the qualitative analysis of two field trials. All three approaches were enabled by the engineering and development of d-touch, an actual recognition system that supports designable visual markers and by its integration in a variety of applications and experimental probes. D-touch is based on image topology, and its markers are defined in terms of constraints on the nesting of dark and light regions. The constraints imposed by d-touch are flexible enough to allow novice users to create markers which are visually expressive and at the same time machine readable. A user study demonstrates how such system enables people to design their own functional visual markers, determining their aesthetic qualities and what they visually communicate to others. A desktop application to support users in the creation of valid markers, the d-touch analyser, is presented and its usefulness is demonstrated through the same study. A formal usability experiment comparing five variations of marker-based interfaces on keypad and touch-screen phones shows that all of them allow users to reliably select targets within, on average, less than 4 seconds. Participants of the experiment reported a strong preference for interfaces that involve only marker scanning, compared to those that require a combination of marker scanning and key-presses or touch selections. Example designs of mobile interface generated by the author as well as others are presented to expose how the d-touch recognition system can be integrated in mobile applications. The examples illustrate a variety of ways in which markers can be used to augment printed materials such as cards, books and product packages, adding to them interactive capabilities. The examples show also different approaches to marker design, ranging from simple and recognisable iconic design, to symbols that integrate cues about the interactive functionality, to making them invisible by hiding them in existing graphics. Finally, the dissertation reports and analyses two field trials conducted to study what practices of physical tagging can emerge from, and be supported by, the use of markers. The trials were centred around the use of uWiki, a functional prototype based on d-touch, that allows users to associate digital content to markers printed on physical tags that can be affixed to objects or buildings. Observations show that a variety of practices emerge around the use of this technology, indicating that they provide a rich medium that has potential to attract the interest of real users. Though the results of this work are preliminary, they serve to demonstrate the range of potential for the future of such systems

    Improving Flood Detection and Monitoring through Remote Sensing

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    As climate-change- and human-induced floods inflict increasing costs upon the planet, both in terms of lives and environmental damage, flood monitoring tools derived from remote sensing platforms have undergone improvements in their performance and capabilities in terms of spectral, spatial and temporal extents and resolutions. Such improvements raise new challenges connected to data analysis and interpretation, in terms of, e.g., effectively discerning the presence of floodwaters in different land-cover types and environmental conditions or refining the accuracy of detection algorithms. In this sense, high expectations are placed on new methods that integrate information obtained from multiple techniques, platforms, sensors, bands and acquisition times. Moreover, the assessment of such techniques strongly benefits from collaboration with hydrological and/or hydraulic modeling of the evolution of flood events. The aim of this Special Issue is to provide an overview of recent advancements in the state of the art of flood monitoring methods and techniques derived from remotely sensed data

    girl.is.a.four.letter.word The Collective Practices of Amateur Self-Imag(in)ing and Personal Website Production 1996 to 2001

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    Scholarship on the practices of young gender-marginalized people online is a burgeoning theme within internet studies and feminist media studies. Within historical scholarship of the internet, young women’s practices have been critically neglected. In feminist art history, feminist practices with emerging technology are abundant but young women making art on and with the web is not. Given the aforementioned gaps, this dissertation aims to expand the interdisciplinary fields of internet studies, feminist media studies, and feminist art history through a genealogy of a conjunctural moment of the world wide web. The thesis title presents the breadth of this project: the erased and forgotten web-based work, specifically the self-imaging practices, of young women who used proto-social media forms in the process, creation, and circulation of production between 1996 and 2001. Demanding a synthesis of critical skills operating within the fields mentioned above, it aims to do so through a phenomenological and affect theory analysis of self-images that appeared on personal websites. It argues that these self-imagi(ni)ng practices serve as (a) tactical methods in reaction to patriarchal regimes of power and s/censorship, (b) a means of engendering the sociality of trauma as a productive orientation, and (c) communicative nodes that through wit(h)nessing reshape a feminist intimate public into a new genre of friendship predicated on the aesthetics and forms of circulation of the work. Most internet analysis misses the aforementioned politically engaged feminist history and its influence on how we use and conceptualize the web today. The project’s objective is to provide a philosophical genealogy of the web, demanding a more politically feminist espousal of it, both in theory and practice

    Inland outports : an interdisciplinary study of medieval harbour sites in the Zwin region

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    The People Inside

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    Our collection begins with an example of computer vision that cuts through time and bureaucratic opacity to help us meet real people from the past. Buried in thousands of files in the National Archives of Australia is evidence of the exclusionary “White Australia” policies of the nineteenth and twentieth centuries, which were intended to limit and discourage immigration by non-Europeans. Tim Sherratt and Kate Bagnall decided to see what would happen if they used a form of face-detection software made ubiquitous by modern surveillance systems and applied it to a security system of a century ago. What we get is a new way to see the government documents, not as a source of statistics but, Sherratt and Bagnall argue, as powerful evidence of the people affected by racism
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