1. An ultrasound system, comprising: an ultrasound acquisition unit including an ultrasound probe for transmitting ultrasound signals to a target object and receiving echo signals, the ultrasound acquisition unit being configured to form a plurality of ultrasound data based on the echo signals; and a processing unit coupled to the ultrasound acquisition unit and configured to form first to N th ultrasound images by using the plurality of ultrasound data, wherein N is a positive integer greater than 1, the processing unit being further configured to estimate a motion degree of the ultrasound probe and process the N th ultrasound image to correct the N th ultrasound image based on the motion degree, wherein the processing unit includes: an ultrasound image forming section configured to form the first to N th ultrasound images based on the plurality of ultrasound data; a motion estimating section configured to estimate a motion degree of the ultrasound probe based on a result of comparing the initially formed first ultrasound image with the N th ultrasound image; and an image processing section configured to extract a portion similar to the first ultrasound image from the N th ultrasound image based on the motion degree and process the N th ultrasound image based on the extracted portion.