1. An intra prediction method of compressing and encoding an image, the method comprising the steps of: comparing an SAD value C calculated from macro block data of a present frame and a previous frame with a reference value K and determining a prediction method; and selectively performing on input macro block data a first method of determining a best mode and a block size by prediction in a plurality of prediction modes based on spatial directivity and generating prediction data and a second method of generating prediction data using the best mode and the block size used in the previous frame, depending on the determined prediction method.