An In-Depth Study on Open-Set Camera Model Identification

Camera model identification refers to the problem of linking a picture to the camera model used to shoot it. As this might be an enabling factor in different forensic applications to single out possible suspects (e.g., detecting the author of child abuse or terrorist propaganda material), many accurate camera model attribution methods have been developed in the literature. One of their main drawbacks, however, is the typical closed-set assumption of the problem. This means that an investigated photograph is always assigned to one camera model within a set of known ones present during investigation, i.e., training time, and the fact that the picture can come from a completely unrelated camera model during actual testing is usually ignored. Under realistic conditions, it is not possible to assume that every picture under analysis belongs to one of the available camera models. To deal with this issue, in this paper, we present the first in-depth study on the possibility of solving the camera model identification problem in open-set scenarios. Given a photograph, we aim at detecting whether it comes from one of the known camera models of interest or from an unknown one. We compare different feature extraction algorithms and classifiers specially targeting open-set recognition. We also evaluate possible open-set training protocols that can be applied along with any open-set classifier, observing that a simple of those alternatives obtains best results. Thorough testing on independent datasets shows that it is possible to leverage a recently proposed convolutional neural network as feature extractor paired with a properly trained open-set classifier aiming at solving the open-set camera model attribution problem even to small-scale image patches, improving over state-of-the-art available solutions.Comment: Published through IEEE Access journa

Camera model identification based on DCT coefficient statistics

International audienceThe goal of this paper is to design a statistical test for the camera model identification problem from JPEG images. The approach relies on the camera fingerprint extracted in the Discrete Cosine Transform (DCT) domain based on the state-of-the-art model of DCT coefficients. The camera model identification problem is cast in the framework of hypothesis testing theory. In an ideal context where all model parameters are perfectly known, the Likelihood Ratio Test is presented and its performances are theoretically established. For a practical use, two Generalized Likelihood Ratio Tests are designed to deal with unknown model parameters such that they can meet a prescribed false alarm probability while ensuring a high detection performance. Numerical results on simulated and real JPEG images highlight the relevance of the proposed approach

2018 IEEE Signal Processing Cup: Forensic Camera Model Identification Challenge

The goal of this Senior Capstone Project was to lead Union College’s first ever Signal Processing Cup Team to compete in IEEE’s 2018 Signal Processing Cup Competition. This year’s competition was a forensic camera model identification challenge and was divided into two separate stages of competition: Open Competition and Final Competition. Participation in the Open Competition was open to any teams of undergraduate students, but the Final Competition was only open to the three finalists from Open Competition and is scheduled to be held at ICASSP 2018 in Calgary, Alberta, Canada. Teams that make it to the Final Competition will be competing to win a grand prize of $5,000. The goal of this year’s competition required teams to build a classification system that used a combination of various signal processing, machine learning, and image forensic techniques in order to determine the make and model of the camera used to capture a digital image both before and after that image has been post processed. IEEE provided competing teams with an image database consisting of ten different camera models and 275 images accompanying each camera for teams with which to use to train their classification systems. This senior project design report focused on the proposed classification system design that was implemented and submitted on behalf of Union’s Signal Processing Cup Team. The chosen classification system design used methods of re-sampling and re-interpolating in order to build feature spaces based on the relative differences of the original and reconstructed images from the provided image database. These feature spaces were then used to train machine learning classifiers in order to develop an ensemble-based decision fusion to identify camera source. Through the completion of this project, students competing in the IEEE Signal Processing Cup gained experience using signal processing, machine learning, and image forensic techniques to solve challenging information security problems

Camera model identification based on the generalized noise model in natural images

International audienceThe goal of this paper is to design a statistical test for the camera model identification problem. The approach is based on the generalized noise model that is developed by following the image processing pipeline of the digital camera. More specifically, this model is given by starting from the heteroscedastic noise model that describes the linear relation between the expectation and variance of a RAW pixel and taking into account the non-linear effect of gamma correction.The generalized noise model characterizes more accurately a natural image in TIFF or JPEG format. The present paper is similar to our previous work that was proposed for camera model identification from RAW images based on the heteroscedastic noise model. The parameters that are specified in the generalized noise model are used as camera fingerprint to identify camera models. The camera model identification problem is cast in the framework of hypothesis testing theory. In an ideal context where all model parameters are perfectly known, the Likelihood Ratio Test is presented and its statistical performances are theoretically established. In practice when the model parameters are unknown, two Generalized Likelihood Ratio Tests are designed to deal with this difficulty such that they can meet a prescribed false alarm probability while ensuring a high detection performance. Numerical results on simulated images and real natural JPEG images highlight the relevance of the proposed approac

Camera model identification based on forensic traces extracted from homogeneous patches

A crucial challenge in digital image forensics is to identify the source camera model used to generate given images. This is of prime importance, especially for Law Enforcement Agencies in their investigations of Child Sexual Abuse Material found in darknets or seized storage devices. In this work, we address this challenge by proposing a solution that is characterized by two main contributions. It relies on the extraction of rather small homogeneous regions that we extract very efficiently from the integral image, and on a hierarchical classification approach with convolutional neural networks as the underlying models. We rely on homogeneous regions as they contain camera traces that are less distorted than regions with high-level scene content. The hierarchical approach that we propose is important for scaling up and making minimal modifications when new cameras are added. Furthermore, this scheme performs better than the traditional single classifier approach. By means of thorough experimentation on the publicly available Dresden data set, we achieve an accuracy of 99.01% with 5-fold cross-validation on the ‘natural’ subset of this data set. To the best of our knowledge, this is the best result ever reported for Dresden data set

RemNet: Remnant Convolutional Neural Network for Camera Model Identification and Image Manipulation Detection

Camera model identification (CMI) and image manipulation detection are of paramount importance in image forensics as digitally altered images are becoming increasingly commonplace. In this thesis, we propose a novel convolutional neural network (CNN) architecture for performing these two crucial tasks. Our proposed Remnant Convolutional Neural Network (RemNet) is designed with emphasis given on the preprocessing task considered to be inevitable for removing the scene content that heavily obscures the camera model fingerprints and image manipulation artifacts. Unlike the conventional approaches where fixed filters are used for preprocessing, the proposed remnant blocks, when coupled with a classification block and trained end-to-end, learn to suppress the unnecessary image contents dynamically. This helps the classification block extract more robust images forensics features from the remnant of the image. We also propose a variant of the network titled L2-constrained Remnant Convolutional Neural Network (L2-constrained RemNet), where an L2 loss is applied to the output of the preprocessor block, and categorical crossentropy loss is calculated based on the output of the classification block. The whole network is trained in an end-to-end manner by minimizing the total loss, which is a combination of the L2 loss and the categorical crossentropy loss. The whole network, consisting of a preprocessing block and a shallow classification block, when trained on 18 models from the Dresden database, shows 100% accuracy for 16 camera models with an overall accuracy of 98.15% on test images from unseen devices and scenes, outperforming the state-of-the-art deep CNNs used in CMI. Furthermore, the proposed remnant blocks, when cascaded with the existing deep CNNs, e.g., ResNet, DenseNet, boost their performances by a large margin. The proposed approach proves to be very robust in identifying the source camera models, even if the original images are post-processed. It also achieves an overall accuracy of 95.49% on the IEEE Signal Processing Cup 2018 dataset, which indicates its generalizability. Furthermore, we attain an overall accuracy of 99.68% in image manipulation detection, which implies that it can be used as a general-purpose network for image forensic tasks

Identificación del modelo de cámara mediante Redes Neuronales Convolucionales

La identificación del modelo de cámara siempre ha sido uno de los campos principales del análisis forense de imágenes, ya que es la base para resolver una amplia gama de problemas forenses. Dado que el Deep Learning ha logrado un gran progreso en las tareas de visión por computador, ha surgido un gran interés en la aplicación del aprendizaje profundo en imágenes forenses. En este documento, se propone un método de identificación de modelo de cámara basado en redes neuronales convolucionales profundas (CNNs). A diferencia de los métodos tradicionales, las CNNs pueden extraer características de forma au-tomática y simultánea y aprender a clasificar durante el proceso de aprendizaje. En el presente trabajo se describe un enfoque de aprendizaje profundo para el problema de detección de cámara entre 3 modelos diferentes como parte del IEEE Signal Processing Cup 2018: Camera Model Identification organizado por IEEE Signal Processing Society. Los experimentos muestran que podemos detectar modelos de cámara desconocidos con una precisión de más del 90%.Source camera model identification has always been one of the main fields of digital image forensics since it is the foundation of solving a wide range of forensic problems. Several effective camera model identification algorithms have been developed for the practical necessity. However, they are mostly based on traditional machine learning methods. Since Deep Learning has made great progress in computer vision tasks, significant interest has arisen in applying Deep Learning in image forensics. In this paper, we propose a camera model identification method based on deep convolutional neural networks (CNNs). Unlike tradi-tional methods, CNNs can automatically and simultaneously extract features and learn to classify during the learning process. In the current work, we describe our Deep Learning approach to the camera detection task of 3 cameras as a part of the IEEE Signal Processing Cup 2018: Camera Model Identification hosted by IEEE Signal Processing Society. Experiments show that we can detect unknown camera models with an accuracy greater than 90%.Universidad de Sevilla. Máster en Ingeniería de Telecomunicació