Upscaling factor estimation on double JPEG compressed images

Resampling detection is one of the most important topics in image forensics. Some methods can even estimate the resampling factors. However, it remains a challenge on the post-compressed images because the JPEG compression destroys the statistical characteristics of the resampled images which greatly affect the detection ability. In this paper, we propose a method to estimate the upscaling factors of double JPEG compressed images in the presence of image upscaling between the two compressions. Both of the pre-compression and the post-compression have a great impact on the estimation. We first analyze the pre-compressed image upscaling and find that the peaks produced by the pre-compression will be suppressed by the post-compression. Therefore, the post-compression has a greater impact than the pre-compression. Through analyzing the influence of post-compression and the causes of the periodic JPEG peaks, we find that the image block estimation can effectively reduce the influence of JPEG block artifacts. To further improve the detection ability, a Gaussian filtering model is developed to deal with JPEG block artifacts and a detector which can more effective extract resampling characteristic is proposed to estimate the upscaling factor. The experimental results demonstrate that the proposed detection method outperforms some state-of-the-art methods.