An image processing apparatus includes a search range providing circuit, a searching circuit and an encoder. The search range providing circuit obtains N number of predicted motion vectors for a target image block, and accordingly sets N number of corresponding search ranges in a reference frame, where N is an integer greater than 1. The searching circuit performs a motion compensation searching process individually on the N search ranges to accordingly determine a motion vector for the target image block. The encoder encodes the target image block according to the motion vector.