At least one image registering unit records at least one series of imagesrepresenting a subject. A control unit controls an operation sequence forthe at least one image registering unit in such a manner that a subsequentdata processing unit receives a repeating sequence of image frames therefrom, wherein each period (P) contains at least one image frame of a firstresolution (501) and at least one image frame of a second resolution (602)being different from the first resolution (501). Based on the registeredimage frames, the data processing unit produces eye/ gaze tracking datawith respect to the subject.