Transparent Image Encryption Using Progressive JPEG

Many application scenarios do not demand confidential encryption of visual data, but on the contrary require that certain image information is public (transparent encryption). One scenario is e.g., PayTV, where a low quality version should become public to attract possible customers. Transparent encryption can be implemented most efficiently in case of scalable bitstreams by encrypting enhancement layer data and baseline JPEG is therefore not well suited for designing such encryption schemes in an efficient manner. This paper investigates how transparent encryption can be realized through selective encryption of the progressive JPEGmodes. The traditional approach which encrypts enhancement layers starting at the end of the bitstream suffers from high computational load. Encryption schemes with significantly reduced encryption effort are shown to deliver equivalent image quality and security.