Patent ID: 8542878

Claim:
Method of controlling a function of a device, including: obtaining a sequence ( 19 ; 34 ; 48 ) of digital images taken at consecutive points in time using a camera; selecting at least one measurement zone ( 25 ) including a plurality of image points; for at least one measurement zone ( 25 ), obtaining a signal ( 30 ; 41 ; 55 ) representative of at least variations in a time-varying value of a combination of pixel values at at least a number of the image points, and determining at least one characteristic of the signal ( 30 ; 41 ; 55 ) within at least a range of interest of its spectrum relative to comparison data, the determination comprising at least one of: (i) determining whether the signal ( 30 ; 41 ; 55 ) has a spectrum with a local maximum at a frequency matching a comparison frequency to a certain accuracy; and (ii) determining whether at least a certain frequency component of the signal ( 30 ; 41 ; 55 ) is in phase with a comparison signal to a certain accuracy; and controlling the function in dependence on whether the determination is positive, wherein the method is unobtrusive to a living being present in a field of view of the camera, and wherein the living being can be in motion.