Reversible Image Thumbnail Preservation With High-Visual Naturalness

With the proliferation of cloud applications, users are increasingly uploading their private images to cloud servers to avail of supplement storage capacity. Unlike image encryption, the thumbnail-preserving technique is a way of safeguarding image privacy and preserving the outline of the thumbnail image, which allows authorized users to recognize it according to prior knowledge of the original image. Recently, several thumbnail-preserving encryption schemes have been proposed. But most of the sum-preserving encryption-based schemes are irreversible, thereby significantly constraining their practical value. Moreover, the visual quality of images generated with the reversible thumbnail-preserving schemes is unsatisfactory, leading to a decrease in the user recognition accuracy. In light of the aforementioned, this article presents an efficient scheme to generate thumbnail-preserving images with high-visual naturalness, while ensuring reversibility of the process. Experimental results demonstrate that the proposed scheme achieves significant visual quality improvements compared to state-of-the-art schemes. Furthermore, the thumbnail-preserving images generated by using our scheme can effectively evade detection by confusing malicious attackers.

I. Introduction

With the prosperity and development of the economy and society, digital image has become a popular medium for capturing and preserving special moments in daily life. Especially in the era of mobile communication, people can easily shoot and store a large number of photographs using their smartphones. Nowadays, cloud storage has flourished. More and more users are uploading their images to cloud servers, such as iCloud, Google Driver, and Dropbox, for flexible access at any time through wired or wireless networks. However, the security vulnerability in the cloud is a critical issue in which the user information disclosure events on the cloud have been occurring continuously. The infamous leak event known as “Celebgate” occurred in 2014, where over five hundred private photographs of various celebrities were disclosed and disseminated, which causing significant turmoil. The reason for these leaks is that the original users’ images are directly stored on the cloud server, so any users who break through the firewall can access the image contents.