The invention provides a method and a system for manipulating an image displayed on a screen (11), where an operator uses e.g. a finger to identify a region of interest (ROI) without touching the screen (11). The spatial position of the finger relative to the screen (11) is detected, i.e. its x, y and z coordinates. A region of interest (ROI) on the screen (11) including the two coordinates (x, y) is selected, and an image property such as contrast in the selected region of interest is changed in dependence on the distance (z) of the movable object (13) from the screen (11). The invention is ideal for manipulating medical images such as X-ray images, but applications in consumer electronics are also conceivable where image processing is performed.