1. A method for ascertaining a heart rate of a driver of a vehicle, comprising: recording, via a camera, a plurality of successive images; analyzing, by processing circuitry, at least one of the plurality of successive images to ascertain an eye position of an eye of the driver in the plurality of successive images; based on the ascertained eye position, selecting, by the processing circuitry, a respective subsection within each of the plurality of successive images that corresponds to a particular subsection of a head of the driver, wherein the subsection is of the eye or is of a region that is defined by a predetermined spatial relationship to the eye; identifying, by the processing circuitry, differences between the subsections with respect to at least one of a size and a color of the respective subsections of the respective images of the plurality of successive images; and based on the identified differences, the processing circuitry ascertaining the heart rate.