The present invention relates to a device, system and method for monitoring a subject. To obtain increased performance at reasonable cost and complexity, the device comprises an input interface (81) configured to obtain image data acquired over time by an imaging unit from a field of view containing at least part of a subject, a monitoring signal determination unit (82) configured to determine a monitoring signal from the obtained image data of the subject, a processing unit (83) configured to evaluate the image data to determine the spatial configuration of the subject with respect to the imaging unit and to generate a feedback signal for providing feedback about the determined spatial configuration, and an output interface (84) configured to output the feedback signal.
