1. A method for segmenting an object within a current digital image frame, comprising the steps of: receiving a set of control points used in deriving an object boundary from a prior image frame, wherein the received set of control points serves as an initial set of control points for the current digital image frame; defining a restricted area within the current digital image frame based on the received set of control points, wherein the restricted area corresponds to a band about the object boundary; updating the initial set of control points to an updated set of control points in response to an operator command; defining a current-frame object boundary for said object of the current digital image frame using the updated set of control points, wherein said step of defining the current-frame object boundary comprises deriving a closed contour connecting each control point of the updated set of control points, wherein only image data within the restricted area are eligible to form the closed contour.