1. Method for authenticating a tag, characterized in that it comprises: a step ( 205 ) of capturing an image, with a communicating mobile terminal, of at least a portion of a tag comprising at least a portion of an identifier; a step ( 210 ) of transmitting said identifier to a server; a step ( 215 ) of reading, from a memory of tag images, the image of a tag having said identifier; a step ( 220 ) of transmitting, to said communicating mobile terminal, at least a portion of the image read from the memory; and a step ( 230 ) of displaying at least a portion of the transmitted image superimposed on an image captured by said terminal, the image resulting from the superimposition of images having, in each of these points, a value that depends at the same time on the value of a point of each of the superimposed images.