1. A method of segmenting an image of an object from an image of an organ, comprising: generating a reference model of the object by using a priori knowledge related to the object of the organ; determining whether a first image of the organ comprises a first area in which a shape of the object is unidentified; in response to determining that the first image excludes the first area, segmenting a second image of the object from the first image; and in response to determining that the first image comprises the first area, estimating a progression direction of the first area from the reference model to segment a second image of the object from the first image.