Privacy-preserving Image Retrieval Scheme Allowing Mixed Use of Lossless and JPEG Compressed Images

We propose a novel content based-image retrieval scheme for encryption-then-compression (EtC) images. In conventional retrieval schemes for EtC images, the JPEG standard was applied to EtC images as a compression method, although EtC images can be applied to both JPEG compression and lossless compression methods such as JPEG-LS. In contrast, the proposed retrieval scheme allows the mixed-use of lossless and lossy-compression methods. In an experiment, the proposed method is demonstrated to maintain a high retrieval performance, even under the mixed-use of lossless- and lossy-compressed EtC images.