Histogram-based retrieval for encrypted JPEG images

This work proposes a novel scheme for encrypted JPEG image retrieval, which includes image encryption and unsupervised/supervised retrieval phases. Using this scheme, the encrypted images are produced by permuting DCT coefficients, and transmitted to a database server. With an encrypted query image, although the server does not know the plaintext content, he may get the histogram at each frequency position. After calculating the distances between the histograms of encrypted query image and database image, the server can return the encrypted images with plaintext content similar to the query image according to integrated distances. If a training image set is available, the retrieval results can be also determined by conditional probabilities calculated from a supervised mechanism.