In this paper, we proposed a passive scheme to achieve image tampering detection. To correctly estimate the
quantization table, each AC DCT coefficient is classified into different types and then the corresponding quantization
stepsize is adaptively measured from its power spectrum density (PSD) and PSD's Fourier transform. Based on the
quantization table estimation, the proposed scheme is composed of pre-screening, candidate region selection, and
tampering region identification. The pre-screening is developed to decide whether an image had been JPEG compressed.
To select candidate regions for estimating quantization table, a seed region is first selected by finding a suitable region
by removing suspicious regions. Based on the seed region, the candidate region can be obtained by suitably merging
other regions into the seed. To avoid merging the suspect regions, a candidate region refinement is performed in the
region growing. After estimating the quantization table from the candidate region, a MLR classifier based on the
inconsistency of quantization table is exploited to identify tampered regions block by block. The experimental results
demonstrate that our proposed scheme can not only estimate the quantization table but also identify tampered regions
This paper presents a public-key-based optical image cryptosystem with adaptive steganography for practical secure communications. The optical image cryptosystem employs a hybrid architecture for ciphering and deciphering in which double random-phase encoding and asymmetric encryption algorithms are utilized for images and session keys, respectively. The session key is safely protected and transmitted by using an asymmetric encryption algorithm and an adaptive steganographic scheme, respectively. To perform the adaptive steganographic scheme, a sorting technique is used to find the suitable embedding position in the embedding domain, a least-significant-bit truncation algorithm is presented to find the invariant hiding order, and a quantization-based data-embedding algorithm is utilized to hide message bits. Experimental results show that the proposed scheme is superior to that of a previous one due to Lin et al., no matter what embedding domain, quantization level, and message size are used. Especially, compared with the latter scheme a large improvement (22.56 dB) of image quality is achieved by using the proposed adaptive steganographic scheme.
A watermarking scheme, proposed to embed both image-dependent and fixed-part marks for dual protection (content
authentication and copyright claim) of JPEG images, is described in this paper. To achieve the goals of efficiency,
imperceptibility, and robustness, a compressed-domain informed embedding algorithm, which adopts Lagrangian
multiplier optimization approach followed by an iterative refinement procedure, is developed. To robustly detect the
fixed-part watermark, a two-stage watermark extraction procedure is devised. At the first stage, the semi-fragile
watermark in each channel is extracted for content authentication. At the second stage, a weighted soft-decision decoder,
in which the signal detected in each channel is weighted according to the estimated channel condition, is used to raise the
recovery rate of the fixed-part watermark for copyright protection. Experimental results manifest that the proposed
scheme can not only achieve the purposes of content authentication (semi-fragile watermarks to resist mild image
alterations and detect malicious tampered regions) and copyright protection (robust watermarks to claim the ownership),
but also maintain higher visual quality (by at least 4 dB than the prior method) at a specified watermark robustness.