PRIMARY QUALITY FACTOR ESTIMATION OF RESIZED DOUBLE COMPRESSED JPEG IMAGES

Reconstructing the image processing chain and the parameters used in each step would provide important forensic clues. Many methods have been designed to estimate the primary quality factor of double compressed JPEG images. However, it is still a challenge to address such problem in the presence of resizing. In this paper, we concentrate on this topic by theoretically analysing the Welch Power Spectral Density (PSD) of the DC coefficients histogram of the counter-resized image. According to the analysis, We find that: i) the most prominent peak of PSD not only dependents on the first quality factor, but also relates to the second one, ii) the peak location nonlinearly maps to the quality factor in the first compression. A simple yet efficient method is proposed to estimate the primary quality factor based on the nonlinear mapping and geometric fitting. Experimental results demonstrate the proposed method provides superior performances.