  In this paper, we propose a privacy-preserving image-retrieval scheme using a
codebook generated by using a plain-image dataset. Encryption-then-compression
(EtC) images, which were proposed for EtC systems, have been used in
conventional privacy-preserving image-retrieval schemes, in which a codebook is
generated from EtC images uploaded by image owners, and extended SIMPLE
descriptors are then calculated as image descriptors by using the codebook. In
contrast, in the proposed scheme, a codebook is generated from a dataset
independent of uploaded images. The use of an independent dataset enables us
not only to use a codebook that does not require recalculation but also to
constantly provide a high retrieval accuracy. In an experiment, the proposed
scheme is demonstrated to maintain a high retrieval performance, even if
codebooks are generated from a plain image dataset independent of image owners'
encrypted images.
