基于条件共生概率矩阵的移位JPEG双压缩检测

针对合成JPEG图像的小区域移位JPEG双压缩(SD-JPEG压缩)篡改问题,提出一种基于条件共生概率矩阵(CCPM)的SD-JPEG压缩篡改检测算法。为了减小图像内容的影响,增强SD-JPEG压缩效应,首先对JPEG量化的离散余弦变换(DCT)系数的幅度矩阵进行水平、垂直、主对角和副对角4个方向差分和阈值化处理,然后使用CCPM对这4个阈值化的差分矩阵进行建模,选取CCPM的元素作为特征数据,并用主分量分析(PCA)对其降维处理,最后通过支持向量机(SVM)技术判决图像块是否经过SD-JPEG压缩。实验结果验证了本文算法的有效性。

Detecting shifted JPEG double-compression based on conditional co-occurrence probability matrix

For the small tampered region coming from two times of JPEG compression with inconsistent block segmentation in composite JPEG images,in this paper,an effective shifted double JPEG(SD-JPEG) compression tampering detection method based on conditional co-occurrence probability matrix(CCPM) is proposed.In order to reduce the effects caused by the diversity of image content and enhance the SD-JPEG compression,difference 2-D arrays are generated along four directions,i.e.,horizontal,vertical,main diagonal and minor diagonal directions,for magnitudes of JPEG quantized discrete cosine transform(DCT) coefficients.The thresholding technique is used to deal with these difference arrays for reducing computational cost.Conditional co-occurrence probability matrix is used to model these thresholded difference 2-D arrays.All elements of these conditional co-occurrence probability matrices are served as features for SD-JPEG compression tampering detection.Principal component analysis(PCA) is introduced to reduce the dimensionality of the proposed features.Support vector machine(SVM) is employed as the classifier to identify whether an image block has been SD-JPEG compressed.Experimental results demonstrate the effectiveness of the proposed method.