1. A method for determining at least one geometric/physiognomic parameter associated with the mounting of an ophthalmic lens in a spectacle frame worn by a user, comprising the following steps: a) placing an accessory on the user's head, said accessory comprising at least one brightness calibration element, said brightness calibration element including at least two contrasted zones; b) capturing an image of the user's head on which said accessory has been placed, using an image capture device; c) determining the position of the image of the brightness calibration element of said accessory on said image captured in step b); d) determining a measured value of the brightness of at least one part of the image of this brightness calibration element; e) modifying a parameter for adjusting the optical image-acquisition conditions of said image capture device as a function of this measured value in such a way as to improve the contrast of the image of the contrasted zones of the calibration element; f) capturing another image with the modified parameter for adjusting the optical acquisition conditions; and g) determining said looked-for geometric/physiognomic mounting parameter on the basis of this other image.