Digital image/video coding standards such as JPEG, H.264 are becoming more and more important for multimedia applications. Due to the huge amount of computations, there are significant efforts to speed up the encoding process. This paper proposes a Laplacian based statistical model to predict zero-quantized DCT coefficients in JPEG and to reduce the computations of encoding process. Compared with the standard JPEG and the reference in the literature, the proposed model can significantly simplify the computational complexity and achieve the best real-time performance at the expense of negligible visual degradation. Moreover, it can be directly applied to other DCT-based image/video codec. Computational reduction also implies longer battery lifetime and energy economy for digital applications.