Image Scramble Algorithm with Robustness under Transcoding

Abstract

In this work, image scramble algorithm is proposed that is robust under transcoding to recover a successfully descrambled image from a scrambled image. The transcoding schemes as such as resizing, color space conversion, color format conversion, etc. are considered as they are commonly applied in multimedia sharing Instant Messaging services (IMs) applications. To combat such transcoding, following methods are applied: MCU block shuffle scramble, restricted DCT coefficient sign randomization, restricted DCT coefficient swap within MCU block, adaptive DCT coefficient scaling and clipping depending on the image and postupdate. The resulting scrambled image yields good visual scramble effects and small increase in bitstream size compared to the original image. The scramble key, that scramble algorithm depends upon, is encrypted with the authorized user information and embedded in the scrambled image, chosen prior to transmission, to successfully descramble the scrambled image without additional servers for key management. These results allow scrambled image to be shared via IMs and descramble successfully without key management servers, thereby possibly creating new multimedia service for smartphones.