1. An image processing apparatus for compressing an input image using a motion vector, the image processing apparatus comprising: means for storing position information of each pixel of a first frame that is earlier in time than a second frame at an address corresponding to a feature value (f) that is based on a value of said each pixel and pixels peripheral to said each pixel, the feature value representing a feature of said each pixel and defined as 
 f(L i−1,j−1 , L i−1,j , L i−1,j−1 , L i,j−1 , L i,j , L i,j+1 , L i+1,j−1 , L i+1,j , L i+1,j+1 ), where i indicates a vertical direction, j indicates a horizontal direction, and L i,j indicates a pixel value of a position (i, j); first means for detecting the position information stored at an address corresponding to a feature value that is based on a value of the target pixel of which a motion vector is to be determined or a pixel peripheral to said target pixel of the second frame, the feature value representing said feature of said target pixel; means for determining a centroid of candidate pixels of the first frame which are identified with the position information detected by the first means for detecting; and second means for detecting a motion vector of the target pixel from the position of the target pixel and the centroid.