1. A method of displaying a 3D image by using a display apparatus, the method comprising: generating an annotation related to a point of the 3D image and determining an image depth of the annotation; generating an indicator which is a segment connecting the annotation and the point and determining a first image depth of a starting point of the segment and a second image depth of an ending point of the segment; determining a size of the annotation based on the image depth of the annotation; displaying the annotation according to the determined size of the annotation and the indicator with the 3D image based on the image depth of the annotation and the first and second image depths of the segment; and when an image depth of the point is changed, keeping the same image depth of the annotation as the changed image depth of the point, wherein the annotation comprises additional information related to the point of the 3D image.