Content-fragile Watermarking Research Articles

Content fragile watermarking based on a computer generated hologram coding technique

In this paper we present a content fragile watermarking based on a computer generated hologram coding technique. Content fragile watermarking techniques aim to prevent tampering and fraudulent use of modified images. A content fragile watermark monitors the integrity of the content of the image but not its numerical representation. Therefore, the watermark is designed so that the integrity is proven if the content of the image has not been tampered with. However, if parts of the image are replaced, the watermark information should indicate evidence of forgery. Using computer generated hologram watermarking, the embedded mark could be easily recovered by means of a Fourier transform. Due to this fact the host image can be tampered with and watermarked with the same holographic pattern. To avoid this possibility we have introduced an encryption method using a private key. The proposed technique is suitable for use for freelancers' photography authentication. It could be applied to colour images as well as to grey-scale ones. The proposed schema is based on the knowledge of the original mark from the authentication entity, to apply image correlation between this and the extracted one.

Watermarking-Based Digital Audio Data Authentication

Digital watermarking has become an accepted technology for enabling multimedia protection schemes. While most efforts concentrate on user authentication, recently interest in data authentication to ensure data integrity has been increasing. Existing concepts address mainly image data. Depending on the necessary security level and the sensitivity to detect changes in the media, we differentiate between fragile, semifragile, and content-fragile watermarking approaches for media authentication. Furthermore, invertible watermarking schemes exist while each bit change can be recognized by the watermark which can be extracted and the original data can be reproduced for high-security applications. Later approaches can be extended with cryptographic approaches like digital signatures. As we see from the literature, only few audio approaches exist and the audio domain requires additional strategies for time flow protection and resynchronization. To allow different security levels, we have to identify relevant audio features that can be used to determine content manipulations. Furthermore, in the field of invertible schemes, there are a bunch of publications for image and video data but no approaches for digital audio to ensure data authentication for high-security applications. In this paper, we introduce and evaluate two watermarking algorithms for digital audio data, addressing content integrity protection. In our first approach, we discuss possible features for a content-fragile watermarking scheme to allow several postproduction modifications. The second approach is designed for high-security applications to detect each bit change and reconstruct the original audio by introducing an invertible audio watermarking concept. Based on the invertible audio scheme, we combine digital signature schemes and digital watermarking to provide a public verifiable data authentication and a reproduction of the original, protected with a secret key.