1. A decision device provided for deciding whether an eye having a macula and an optical axis is real or false, said decision device comprising: a light emitting an infrared flux towards the eye along an entry axis; an infrared camera capturing an image of the eye along an exit axis, the entry axis and the exit axis being aligned with the optical axis so that the macula illuminated by the light under the incidence of the entry axis is seen by the camera; processor detecting, on an image captured by the camera, whether a peripheral zone representing the iris exists and whether a central zone in the peripheral zone, a colour of which is representative of the existence of the macula, exists, and delivering information representing this detection; a decider deciding whether the eye is real or false according to the information delivered by the processor; a tracker tracking a face of an individual passing in front of the light and the camera, in order to locate an eye on this face and to determine the direction of the optical axis of this eye; a positioner controlled by the tracker and aligning the entry axis, the exit axis and the optical axis; a displacer controlled by the tracker and offsetting the entry axis and the exit axis with respect to the optical axis so that, even if the macula remains partly illuminated by the light, it is no longer seen by the camera, wherein the light has an emission direction, the camera has a reception direction, the emission direction and the reception direction are vertical, the optical axis is horizontal, the positioner comprises firstly a base on which a 45° mirror is mounted, disposed vertically above the light and the camera, and secondly a linear displacer provided for linearly moving the base parallel to the emission direction, and the displacer comprises an angular displacer mounted on the base and carrying the mirror.