1. A method, comprising: displaying a background image on a display screen; receiving, from an input device, a signal indicative of a free hand line being drawn over the background image, wherein the signal includes coordinates of points of the free hand line with respect to the display screen and the free hand line is independent of content represented in the background image; storing the signal in a storage device; determining a principal direction of the free hand line based on the signal; determining a radius of curvature of the free hand line based on the principal direction of the free hand line; comparing the determined radius of curvature with predetermined line stiffness criteria; successively removing points from the storage device in response to the determined radius of curvature not satisfying the predetermined line stiffness criteria; generating a smooth stiff line based on the stored signal; and displaying the smooth stiff line over the background image.