A sensor for venous networks of a part of a living body, having an infrared illumination source, a waveguide illuminated by the infrared illumination source and having, on one face, at least one extraction zone intended to extract the infrared rays from the waveguide in at least one main extraction direction, an image acquisition means disposed opposite the one face so as to define between them a passage through the entrance of which the part of the living body can enter, and having a sensitive element, the or each extraction zone being such that the or each main extraction direction of the extraction zone oriented so as not to intercept the sensitive element.