An image processing method is used for determining a motion vector of a covered/uncovered area within an interpolated picture when picture interpolation is performed. The interpolated picture includes a plurality of blocks, and the image processing method includes: generating a first motion vector and a second motion vector of a block within the interpolated picture; determining which one of the covered and uncovered areas the block is located in, and calculating a reference vector according to the first and second motion vectors; and determining a motion vector of the block according to the reference vector, wherein the reference vector is obtained from vector calculation of the first and second motion vectors using the principle of similar triangles.