  Storage requirements for visual data have been increasing in recent years,
following the emergence of many new highly interactive, multimedia services and
applications for both personal and corporate use. This has been a key driving
factor for the adoption of cloud-based data outsourcing solutions. However,
outsourcing data storage to the Cloud also leads to new challenges that must be
carefully addressed, especially regarding privacy. In this paper we propose a
secure framework for outsourced privacy-preserving storage and retrieval in
large image repositories. Our proposal is based on a novel cryptographic
scheme, named IES-CBIR, specifically designed for media image data. Our
solution enables both encrypted storage and querying using Content Based Image
Retrieval (CBIR) while preserving privacy. We have built a prototype of the
proposed framework, formally analyzed and proven its security properties, and
experimentally evaluated its performance and precision. Our results show that
IES-CBIR is provably secure, allows more efficient operations than existing
proposals, both in terms of time and space complexity, and enables more
realistic, interesting and practical application scenarios.
