At least one image registering unit records at least one series of images representing a subject. A control unit controls an operation sequence for the at least one image registering unit in such a manner that a subsequent data processing unit receives a repeating sequence of image frames there from, wherein each period contains at least one image frame of a first resolution and at least one image frame of a second resolution being different from the first resolution. Based on the registered image frames, the data processing unit produces eye/gaze tracking data with respect to the subject.