The invention relates to a system for determining whether the interior of a vehicle is occupied. The inventive device comprises image acquisition means (10) for acquiring images of an area of the vehicle interior, an image acquisition data generation unit (14) for generating image acquisition data in which every image point of a three-dimensional surface image is presented as a vector in an acquisition coordinate system of the image acquisition means, and a conversion unit (16) that converts the image acquisition data to vehicle image data. Said vehicle image data describe every image point as a vector in a coordinate system that is specific of the vehicle.