In a method and a system for authenticating an object marked with XRF marking, a wavelength spectral profile is provided of a detected portion of an X-Ray signal arriving from an object in response to X-Ray or Gamma-Ray radiation applied to the object and the wavelength spectral profile is filtered to suppress trend and periodic components from the wavelength spectral profile to obtain a filtered profile with improved signal to noise or signal to clutter ratio. The object can be authenticated by processing the filtered profile and identifying one or more peaks therein, which satisfy a predetermined condition, whereby the wavelengths of the identified peaks are indicative of the signatures of materials included in the object.