Now showing 1 - 7 of 7
  • Publication
    Using entropy for image and video authentication watermarks
    ( 2006)
    Thiemert, S.
    ;
    Sahbi, H.
    ;
    Steinebach, M.
    There are several scenarios where the integrity of digital images and videos has to be verified. Examples can be found in videos captured by surveillance cameras. In this paper we propose a semi-fragile watermarking scheme, which can be applied on still images as well as on digital videos. We concentrate on the protection of I-frames in compressed MPEG-1/2 videos. We use the entropy of the probability distribution of gray level values in block groups to generate a binary feature mask, which is embedded robustly into an adjacent I-frame. The approach can distinguish between content-preserving and content-changing manipulations. Positions of content-changing manipulations can be localized. We provide experimental results to analyze the effectiveness of the scheme. In the evaluation part we concentrate on the robustness against content-preserving and the sensitivity to content-changing manipulations.
  • Publication
    A digital watermark for vector-based fonts
    ( 2006)
    Thiemert, S.
    ;
    Steinebach, M.
    ;
    Wolf, P.
    In this paper we present a blind watermarking scheme for vector-based fonts. The scheme can be used for authenticating the copyright holder as well as for identifying customers of fonts. We slightly modify the symmetry between curve pairs to embed a binary message. The watermark is invisible and robust against conversion into other vector-based font formats. An implementation for TrueType-Fonts was evaluated by typeface designers. Based on the blind watermarking scheme we discuss an extension to a non-blind watermark, which is in addition robust against uniform scaling.
  • Publication
    Applying interest operators in semi-fragile video watermarking
    ( 2005)
    Thiemert, S.
    ;
    Sahbi, H.
    ;
    Steinebach, M.
    In this article we present a semi-fragile watermarking scheme for authenticating intra-coded frames in compressed digital videos. The scheme provides the detection of content-changing manipulations while being moderately robust against content-preserving manipulations. We describe a watermarking method based on invariant features referred to as interest points. The features are extracted using the Moravec-Operator. Out of the interest points we generate a binary feature mask, which is embedded robustly as watermark into the video. In the verification process we compare the detected watermark with the interest points from the video to be verified. We present test results evaluating the robustness against content-preserving manipulations and the fragility in terms of content-changing manipulations. Beside the discussion of the results we propose a procedure to provide security of the scheme against forgery attacks.
  • Publication
    Digitale Wasserzeichen als Träger von Metainformation für Geographische Informationssysteme
    ( 2004)
    Thiemert, S.
    ;
    Liu, H.
    ;
    Rauch, M.
    ;
    Pfannkuche, R.
    ;
    Fahrion, R.
    ;
    Steinebach, M.
  • Publication
    Feature-based watermarking scheme for MPEG-I/II video authentication
    ( 2004)
    Dai, Y.
    ;
    Thiemert, S.
    ;
    Steinebach, M.
    This paper presents a new content-fragile watermarking algorithm for the detection and localization of malicious manipulations of MPEG-I/II videos. While being fragile to malicious manipulations, the watermarking scheme is robust against content-preserving manipulations like re-encoding processes. It is a bitstream watermarking method based on 8×8 DCT blocks. One of the main advantages of our scheme is the possibility of localizing positions within the video where modifications occurred. Another main advantage is the portability of the scheme to other multimedia documents based on the 8×8 DCT block domain, e.g. JPEG images. The framework of the watermarking scheme can be divided into three main parts: watermark construction, watermark embedding and watermark detection. We derive a Content Based Message (CBM) from the multimedia document, based on a partial energy relationship between two groups of DCT blocks. Embedding the CBM is based on the Differential Energy Waterma rking (DEW) concept. In the detection process we compare the CBM and the retrieved watermark to detect and locate manipulations. Besides the algorithm we present experimental results to demonstrate the feasibility of the scheme. We discuss four experiments representing four typical kinds of malicious manipulations.
  • Publication
    A high-capacity block based video watermark
    ( 2004)
    Thiemert, S.
    ;
    Vogel, T.
    ;
    Dittmann, J.
    ;
    Steinebach, M.
  • Publication
    Ausgewählte Angriffe der Stirmark Benchmark Suite
    ( 2002)
    Lang, A.
    ;
    Thiemert, S.
    ;
    Steinebach, M.
    ;
    Dittmann, J.