Lossless data hiding in JPEG bitstream

This paper proposes a method of embedding secret data into JPEG bitstream by Huffman code mapping. Although JPEG defined 162 different variable length code (VLC) for AC coefficients, many codes are not used during image compression. According to the statistical results of VLC usage in a cover, we map the unused codes to used codes. The relationships of code mapping are performed by modifying the Huffman values defined in the file header. During data hiding, we replace the codes appearing in bitstream by the mapped codes according to the secret bits. The proposed embedding method preserves the image with no quality distortion and provides more embedding capacity.

► We propose a lossless data hiding method of embedding secret bits into JPEG bitstream by Huffman code mapping. ► Unused variable length codes (VLCs) are mapped to the used codes. ► Relationships of code mapping are performed by modifying the Huffman values defined in the file header. ► We replace the codes appearing in bitstream by the mapped according to the secret bits. The proposed method preserves the image with no quality distortion and provides more embedding capacity.