The classification of microcirculation can be based on the size of the capillary and the velocity of the blood flow. For each type of microcirculation, the ad hoc method is required to measure the blood flow velocity. In this paper, the correlation method is used to measure blood flow velocity in the small-size capillary. The large-size capillaries are classified into three types based on the blood velocities, say low-speed, high-speed, and unstable one. The template-matching algorithm, the Fast Fourier Transform algorithm and a high-speed video camera measurement are used to measure the blood velocities corresponding to those three types of large-size capillary. It was shown by several experiments that fairly good results for different types of capillary may be obtained by using the proposed three image processing algorithms.