The present invention concerns a method and device for detecting the orientation of an area (DO) of the body of an individual placed on an apposition area (AP) of a biometric sensor mounting (P) designed to form a first image (I1) of the area (DO) of the body by total reflection of radiation on the apposition area (AP), and a second image (I2) of the area (DO) of the body from radiation able to pass through the tissues of the body and to be reflected on haemoglobin. The method is characterized in that it comprises a step of determining in a reference frame firstly the longitudinal axis (A) of the area of the body depicted in the first image and secondly two longitudinal edges (B1, B2) of the area of the body depicted in the second image, and a step of determining the orientation of the area of the body with respect to the mounting from the measurement of the relative positions of the two edges (B1, B2) and the axis (A) thus determined in the reference frame. The present invention also concerns a biometric sensor and an installation for identifying an individual comprising such a device.