Huajian Liu

Cell phone camera ballistics: attacks and countermeasures

Multimedia forensics deals with the analysis of multimedia data to gather information on its origin and authenticity. One therefore needs to distinguish classical criminal forensics (which today also uses multimedia data as evidence) and multimedia forensics where the actual case is based on a media file. One example for the latter is camera forensics where pixel error patters are used as fingerprints identifying a camera as the source of an image. Of course multimedia forensics can become a tool for criminal forensics when evidence used in a criminal investigation is likely to be manipulated. At this point an important question arises: How reliable are these algorithms? Can a judge trust their results? How easy are they to manipulate? In this work we show how camera forensics can be attacked and introduce a potential countermeasure against these attacks.

Robust image obfuscation for privacy protection in Web 2.0 applications

We present two approaches to robust image obfuscation based on permutation of image regions and channel intensity modulation. The proposed concept of robust image obfuscation is a step towards end-to-end security in Web 2.0 applications. It helps to protect the privacy of the users against threats caused by internet bots and web applications that extract biometric and other features from images for data-linkage purposes. The approaches described in this paper consider that images uploaded to Web 2.0 applications pass several transformations, such as scaling and JPEG compression, until the receiver downloads them. In contrast to existing approaches, our focus is on usability, therefore the primary goal is not a maximum of security but an acceptable trade-off between security and resulting image quality.

Improved Fourier domain patchwork and template embedding using spatial masking

Robustness against distortions caused by common image processing is one of the essential properties for image watermarking to be applicable in real-world applications. Typical distortions include lossy JPEG compression, filtering, cropping, scaling, rotation, and so on, among which geometric distortion is more challenging. Even slight geometric distortion can totally fail the watermark detection through de-synchronization. Another important property is the watermark payload. Although one-bit watermark is widely used in research work for algorithm testing and evaluation, only checking whether a specific watermark exists does not meet the requirement of many practical applications. This paper presents a practical robust image watermarking algorithm which combines template embedding and patchwork watermarking in Fourier domain. The embedded template enables the necessary robustness against geometric distortions and the patchwork approach provides a reasonable watermark payload which can meet the requirement of most applications. A spatial perceptual mask is used to reshape the embedded energy after it is inverted to the spatial domain, which significantly improves the image quality and enhances the robustness of both template and watermark. Implementation issues and solutions, e.g. fine-tuning of embedding energy of individual pixels, are also discussed. Experimental results demonstrate the effectiveness and practicability of the proposed algorithm.

ForBild: efficient robust image hashing

Forensic analysis of image sets today is most often done with the help of cryptographic hashes due to their efficiency, their integration in forensic tools and their excellent reliability in the domain of false detection alarms. A drawback of these hash methods is their fragility to any image processing operation. Even a simple re-compression with JPEG results in an image not detectable. A different approach is to apply image identification methods, allowing identifying illegal images by e.g. semantic models or facing detection algorithms. Their common drawback is a high computational complexity and significant false alarm rates. Robust hashing is a well-known approach sharing characteristics of both cryptographic hashes and image identification methods. It is fast, robust to common image processing and features low false alarm rates. To verify its usability in forensic evaluation, in this work we discuss and evaluate the behavior of an optimized block-based hash.

Efficient Cropping-Resistant Robust Image Hashing

A digital forensics examiner often has to deal with large amounts of multimedia content during an investigation. One important part of such an investigation is to identify illegal material like pictures containing child pornography. Robust image hashing is an effective technique to help identifying known illegal images even after the original images were modified by applying various image processing operations. However, some specific operations lead to increased false negative rates when using robust image hashing. One of the most challenging operations today is image cropping. In this work we introduce an approach to counter cropping operations on images by combining image segmentation and efficient block mean image hashing. We show that we are able to achieve high detection rates for images where cropping operations where applied on the original known source. This further improves the robustness of our image hashing approach.

FaceHash: Face Detection and Robust Hashing

In this paper, we introduce a concept to counter the current weakness of robust hashing with respect to cropping. We combine face detectors and robust hashing. By doing so, the detected faces become a subarea of the overall image which always can be found as long as cropping of the image does not remove the faces. As the face detection is prone to a drift effect altering size and position of the detected face, further mechanisms are needed for robust hashing. We show how face segmentation utilizing blob algorithms can be used to implement a face-based cropping robust hash algorithm.

On the Reliability of Cell Phone Camera Fingerprint Recognition

Multiple multimedia forensic algorithms have been introduced allowing tracing back media copies back to its source by matching artifacts to fingerprint databases. While this offers new possibilities for investigating crimes, important questions arise: How reliable are these algorithms? Can a judge trust their results? How easy are they to manipulate? It has been shown that forensic fingerprints of digital cameras can be copied from one image to the next. Our aim is to develop new concepts for increasing the security of theses algorithms. In this work, we describe the state of our research work regarding attacks against forensics and provide an outlook on future approaches to increase their reliability.

A ROI-based self-embedding method with high recovery capability

In this paper, a novel block-wise fragile image watermarking algorithm for tampering localization and recovery is proposed. The image is divided into Region of Interest (ROI) and Region of Non Interest (RONI). Considering the ROI-based self-embedding problem as a special erasure channel, fountain code is applied in our method to deal with the reference symbols loss. And to minimize quality degradation in ROI, the reference symbols for recovery are only embedded into RONI blocks. Theoretical analysis shows that the result is nearly optimal, and the experimental results demonstrate the proposed method can offer low payload and high tamper tolerance. And the quality of both the watermarked image and the reconstructed image is high.

Video Watermarking Scheme with High Payload and Robustness against Geometric Distortion

Besides copyright protection, digital video watermarking is also applied in non-security applications like second screen annotation, where high robustness against geometric distortions and high watermark payload are required. Robustness against geometric distortions, however, is still one of the major challenging issues in video watermarking, in particular for the schemes in compressed domain. In this paper, we propose a video watermarking scheme that can resist geometric attacks. The watermark embedding is performed in Fourier domain using patchwork method which is able to handle high embedding payload. Fast transform between block DCT and DFT enables the proposed scheme to be applicable directly in the compressed domain, significantly reducing the computation cost. Perceptual masking is applied in both DFT and DCT domains to ensure high visual quality. Experimental results demonstrate that the proposed scheme achieves satisfactory robustness against all kinds of attacks, including geometric distortions and frame dropping and swapping.

Semantically extended digital watermarking model for multimedia content

Most current watermarking algorithms utilize syntactic features to achieve a good tradeoff between robustness and transparency by using perceptual models. They focus only on a detailed view of the contents, while little attention is paid to define and apply the semantic content features in the watermarking schemes.