Editorial preface: special issue on multimedia data annotation and retrieval using web 2.0

Currently, more than 80 % of the information exchanged on the Web carry personal data and are primarily of multimedia nature (video, audio, images, etc.). Two main reasons are behind this phenomenon: 1) each of the major players on the Internet (individual users, companies, local and/ or regional authorities, etc.) is both data producer and data consumer at the same time, and 2) the use of various tools ofWeb 2.0 (blogs, social networks, etc.) allows to ease sharing, accessing, and publishing information on the Web. While such tools provide users many easy-to-use functionalities, several issues, however, remain unaddressed. For instance, how to automate the processes of annotation and description of some photos using the annotations/descriptions provided by the user friends on his/her blog/wiki/social network? How to provide the user with more effective and expressive means to multimedia information retrieval? How to protect a multimedia data repository (e.g., photo album) while several related information about the same content is already published (by some user friends) on the same or other blog/wiki/social network? This special issue seeks to assess the current approaches and technologies, as well as to outline the major challenges and future perspectives, related to the use ofWeb 2.0 in providing automatic annotation and easing retrieval and access control of multimedia data. It aims to provide an overview of the state of the art and future directions in this field, by including interdisciplinary contributions from various research groups. All the papers we received for this special issue have been submitted to an independent peer reviewing and reviewed by at least three experts.