An image-processing method is characterized by including a searching operation of searching for a local motion vector from each of blocks in the plural images, an electing operation of electing a representative motion vector from the local motion vectors of the respective blocks, and an approximating operation of approximating a motion vector distribution on the images based on the representative motion vector in order to detect motion between plural images with high precision without increasing the number of blocks made by dividing an image. In addition, when an approximate surface thereof is a plane, the operation amount for approximating the motion vector distribution and the information amount for representing the motion vector distribution can be minimized.