1. A method of displaying an image showing an object, the method comprising: displaying a model corresponding to the object; receiving a user input for selecting, from the model, a region of interest (ROI) included in the object; and displaying an image showing the ROI based on the user input, wherein the receiving of the user input comprises receiving a user input for selecting two different points in the model, generating a vector based on the received the user input, identifying a cross-section of the object corresponding to the vector, and setting the cross-section of the object as the ROI, wherein the model is formed by projecting a 3D shape of the object onto a plane.