1. A validation method implemented by a validation device comprising a light source emitting at one wavelength or at a plurality of wavelengths, a sensor, and circuitry adapted to implement an analysis module and a decision-taking module, said validation method comprising: positioning a surface of said element so that it is placed in front of the light source and the sensor; illuminating said element by the light source; capturing, by said sensor, for each wavelength emitted by the light source, an image of said element thus positioned that encompasses an illuminated zone of said element directly illuminated by the light beam emitted by the light source and a peripheral zone, referred to as the diffusion zone of said element, which is peripheral to said illuminated zone; performing an analysis each image thus captured; and deciding as to whether said element is covered with a true skin according to the results of the analysis wherein the analysis comprises, for each captured image, dividing an analysis zone covering the illuminated zone and the diffusion zone into a plurality of calculation zones, establishing for each calculation zone an average intensity, an intensity curve and an intensity gradient curve according to the distance from the calculation zone to the boundary of the illuminated zone, and comparing characteristics of these curves with those extracted from reference curves.