1. A computer-implemented method of controlling a system, comprising: receiving from a user an image of a workpiece or an instruction to automatically generate an image of the workpiece; displaying the image to the user on a display screen; receiving a first input from the user, the first input indicating a position of a user-selectable computer-generated graphic component having an associated functionality, wherein the indication of said position is made relative to the image, and said functionality comprises specifying at least one action to be performed after the graphic component has been positioned; displaying to the user the position of the graphic component relative to the image by overlaying the display of the image with the graphic component based on the position indicated by the first input; receiving a second input from the user, the second input causing the system to execute the functionality associated with the graphic component, the at least one action performed being defined at least in part by a geometric characteristic of the graphic component other than the location of the graphic component, the at least one action specified by the functionality comprising (i) locating or measuring a feature within the image or (ii) an action performed on the imaged workpiece corresponding to the portion of the image overlaid by the graphic component.