Content-Based Image Retrieval in Cloud Using Watermark Protocol and Searchable Encryption

-With the development of the imaging devices, such as digital cameras, smartphones, and medical imaging equipments, our world has been witnessing a tremendous growth in quantity, availability, and importance of images. The needs of efficient image storage and retrieval services are reinforced by the increase of large-scale image databases among all kinds of areas. Compared with text documents, images consume much more storage space. Hence, its maintenance is considered to be a typical example for cloud storage outsourcing. For privacy-preserving purposes, sensitive images, such as medical and personal images, need to be encrypted before outsourcing, which makes the CBIR technologies in plaintext domain to be unusable. In order to secure the data in cloud, the proposed system supports CBIR over encrypted images without leaking the sensitive information to the cloud server. Firstly, feature vectors are extracted to represent the corresponding images. After that, the pre-filter tables are constructed by locality-sensitive hashing to increase search efficiency. Moreover, the feature vectors are protected by the secure kNN algorithm, and image pixels are encrypted by a standard stream cipher. In addition, considering the case that the authorized query users may illegally copy and distribute the retrieved images to someone unauthorized, a watermark-based protocol is used to deter such illegal distributions. In watermark-based protocol, a unique watermark is directly embedded into the encrypted images by the cloud server before images are sent to the query user. Hence, when an illegal image copy is found, the unlawful query user who distributed the image can be traced by the watermark extraction.