By taking pixels of image sequences as moving gas molecules, a novel concept, image temperature, is proposed to describe the natural property of the image motion. The idea comes from the revelation of the Maxwell-Boltzmann Distribution Law in gas dynamic theories. Furthermore, another concept of energy flow corresponding to the optical flow is developed, and the method of the energy flow equation (EFE) is established to estimate image motion. The experiment indicates a better performance of the proposed EFE scheme with significantly reduced false motion estimates when compared to the traditional optical flow equation (OFE).