A foreground image is overlaid over a background image on a visual display. Specifically, an ultrasound signal is transmitted toward a target to be displayed in two dimensions. Echoes of the ultrasound signal are received from the target. Two-dimensional target data acquired from the received echoes are stored. The two-dimensional target data are presented on the visual display as a background image. Part of the target data are overlaid over the background image as a foreground image on the visual display. The size of the foreground image vis-a-vis the background image is changed by the user to permit better observation of an area of interest. Preferably, the size of the foreground image is changed without changing the area occupied by the foreground image on the visual display, which permits the invention to simulate the action of a magnifying glass. The user moves a cursor on the visual display to the center of an area of interest. The user then opens up a window about the cursor to define the length and width of the foreground image on the visual display, while observing the target data presented on the visual display. The user can then magnify the size of the foreground image centered on the cursor, chance the dimensions of the window, and/or change the location of the cursor to move the area of interest, without disturbing the background image.