1. A method for authenticating a current tag, the method comprising: capturing a current image, with a communicating mobile terminal, of at least a portion of the current tag, the captured current image comprising at least a portion of an identifier visible to the naked eye, printed on the tag, the identifier being disposed over at least two hologram elements or diffractive elements; transmitting the captured current image including said identifier to a server; reading, from a memory of tag images, a previously-stored image of a previously-captured tag having a same identifier as the identifier of the current tag; determining the distances of each hologram element or diffractive element to regularly-spaced positions on the previously-captured tag, at the server; comparing the determined distances to distances of each hologram element or diffractive element to regularly-spaced positions on the image captured by the terminal; transmitting, to said communicating mobile terminal, at least a portion of the previously-stored image read from the memory and the result of the comparison; and displaying at least a portion of the transmitted portion of the previously-stored image superimposed on the current image captured by said terminal, a superimposition image resulting from a superimposition of the current image and the transmitted portion of the previously-stored image on a point-to-point basis.