合成图像的篡改对象和背景区域一般来源于不同的JPEG图像。为了快速有效地检测这种图像篡改,提出了一种盲检测JPEG合成图像的方法。首先将图像与Laplacian模板卷积得到二阶差分图像，沿水平（垂直）方向平均后进行离散Fourier变换得到归一化的频谱，基于频谱幅值构造JPEG块效应测度；然后将待检测图像重叠分块并计算其相应块效应测度，利用块效应不一致性检测篡改区域。实验结果表明,该方法是快速有效的。

When creating a digital forgery,it is often necessary to combine several images which were originally of different JPEG compression qualities.This paper proposes a passive approach to detect digital forgeries by checking inconsistencies of blocking artifact.We calculate the second-order difference edge map by convolving the blocky image with a Laplacian kernel.Then compute the mean of the results along the horizontal (vertical) direction and obtain a vector.Discrete Fourier transform of this vector produces a normalized spectrum curve and builds a blocking artifact measure.Divide the composite image into overlapped blocks and calculate the measure of each block.The forged area can be effectively exposed by checking inconsistencies of blocking artifact.Simulation results show the efficiency of proposed algorithm.