1. An image processing apparatus for compressing an input image using a motion vector, the image processing apparatus comprising: storing means for storing position information of pixels of a first frame that is earlier in time than a second frame for each address corresponding to a feature of each pixel; first detecting means for detecting the position information stored at an address corresponding to a feature of a target pixel of the second frame; determining means for determining a centroid of candidate pixels of the first frame which are identified with the position information detected by the first detecting means; and second detecting means for detecting a motion vector of the target pixel from the position of the target pixel and the centroid.