1. An estimation method of a predicted motion vector for an image block having one or more pixels, the estimation method comprising: calculating a pixel difference value corresponding to a current frame and a reference frame which is generated based on at least one frame preceding to the current frame, for each pixel of the image block; determining a pixel difference area corresponding to the current frame and the reference frame according to the pixel difference values corresponding to the plurality of pixels; and determining a predicted motion vector of the image block according to the pixel difference area corresponding to the current frame and the reference frame, wherein the step of determining the predicted motion vector of the image block comprises: determining at least one of a horizontal component and a vertical component of the predicted motion vector, according to at least one of a horizontal length and a vertical length of the pixel difference area.