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International audience; In the last few years, with the increasing popularity of cloud computing and the availability of mobile smart devices as well as ubiquitous network connections, more and more users are uploading their personal data to remote servers. However, this can lead to significant security breaches, where confidentiality, integrity and authentication are constantly threatened. To overcome these multiple problems, multimedia data must be secured, for example by means of encryption before transmission and storage. In this survey, we look into the issues involved in handling encrypted multimedia data, and more specifically we focus on reversible data hiding in encrypted images (RDHEI). The aim of this survey is to present the birth and evolution of RDHEI methods over the last 12 years. We first highlight different classes and characteristics of RDHEI, then describe representative RDHEI methods. A comparison table is presented to summarize the key features and achievements of each representative RDHEI method considered in this survey. Finally, we share the future outlook of emerging applications and open research topics relevant to RDHEI for the next 12 years and beyond.

International audience; Perceptual hashing is conventionally used for content identification and authentication. It has applications in database content search, watermarking and image retrieval. Most countermeasures proposed in the literature generally focus on the feature extraction stage to get robust features to authenticate the image, but few studies address the perceptual hashing security achieved by a cryptographic module. When a cryptographic module is employed [1], additional information must be sent to adjust the quantization step. In the perceptual hashing field, we believe that a perceptual hashing system must be robust, secure and generate a final perceptual hash of fixed length. This kind of system should send only the final perceptual hash to the receiver via a secure channel without sending any additional information that would increase the storage space cost and decrease the security. For all of these reasons, in this paper, we propose a theoretical analysis of full perceptual hashing systems that use a quantization module followed by a crypto-compression module. The proposed theoretical analysis is based on a study of the behavior of the extracted features in response to content-preserving/content-changing manipulations that are modeled by Gaussian noise. We then introduce a proposed perceptual hashing scheme based on this theoretical analysis. Finally, several experiments are conducted to validate our approach, by applying Gaussian noise, JPEG compression and low-pass filtering.

International audience; Data hiding has become increasingly important for many applications, like confidential transmission, video surveillance, military and medical applications. In this paper we present a new approach of 3D object data hiding without changing the position of vertices in the 3D space. The main idea of the proposed method is to find and to synchronize particular areas of the 3D objects used to embed the message. The embedding is carried out by changing the connectivity of edges in the selected areas composed of quadruples. The proposed approach of data hiding in 3D objects is based on minimum spanning tree (MST). This method is lossless in the sense that the positions of the vertices are remaining the same before and after embedding. Moreover the method is blind and does not depend of the order of the data in the files. This approach is very interesting when the 3D objects have been digitalized with high precision.

This paper presents a new approach for reconstructing images mapped or painted on straight uniform generalized cylinders (SUGC). A set of monocular images is taken from di!erent viewpoints in order to be mosaiced and to represent the entire scene in detail. The expressions of the SUGC's projection axis are derived from two cross-sections projected onto the image plane. Based on these axes we derive the SUGC localization in the camera coordinate system. We explain how we can "nd a virtual image representation when the intersection of the two axes is matched to the image center. We analyze the perspective distortions when #attening a scene which is mapped on a SUGC. We evaluate the lower and the upper bounds of the necessary number of views in order to represent the entire scene from a SUGC, by considering the distortions produced by perspective projection. A region matching based mosaicing method is proposed to be applied on the #attened images in order to obtain the complete scene. The mosaiced scene is visualized on a new synthetic surface by a mapping procedure. The proposed algorithm is used for the representation of mural paintings located on SUGCs with closed cross-sections (circles for columns), or opened cross-sections (ellipses or parabolas for vaults). 2001 Pattern Recognition Society. Published by Elsevier Science Ltd. All rights reserved.

In this paper we present a method to localize a cylindral surface with only one perspective view. Based on a priori knowledge we find two axes in the image in order to obtain the three rotation angles between the cylindrical surface coordinate system and the camera coordinate system. Various applications of the proposed method are presented.