1. A method for identifying and authenticating different objects or substances, the method using a computer system coupled to spectrophotometry means, said method comprising at least the two following successive phases: an initial phase comprising: choosing a plurality of chemical markers which, when excited by an incident light ray, emit energy radiations whose frequency spectra can be distinguished from one another and with respect to objects and substances in which they are intended to be incorporated, allocating then incorporating, in each of the objects or substances, a combination of markers that is different than combinations allocated to the other objects or substances, determining an authentication code for each of the objects or substances defined using parameters comprising at least the presence or absence of markers in the allocated combination of markers, storing, a memory of the computer system, the authentication code of all the objects or substances and of related data corresponding to said objects or substances, allocating an identification code to each of said objects or substances, said identification code being associated with at least one of said objects or substances and a recipient or packaging for the at least one of said objects or substances, storing, in the memory of said system, the identification codes for each of the objects or substances, defining a correspondence between the identification codes and the authentication codes, an identification and authentication phase by said system comprising: determining a theoretical identification code for one of said objects or substances by reading the identification code associated with said one of the objects or substances and the recipient or packaging for the object or substance, spectrophotometric analyzing at least part of the one object or substance so as to detect said above parameters, and determining an experimental authentication code of the one object or substance, authenticating said one object or substance if the theoretical identification code corresponds to the experimental authentication code, emitting a validation signal if a correspondence is detected or an alert signal if the experimental authentication code does not correspond to the theoretical identification code, wherein said spectrophotometric analysis comprises the following steps: determining zones of the spectrum to be analysed and the different parameters allocated to each of these zones using said above identification codes, irradiating the one object or substance with a light ray emitted by a generator, sending transmitted or reflected waves onto a dispersing element which deflects them so as to obtain a light spectrum of the light intensity in said zones of the spectrum corresponding to different wavelength ranges, detecting the light intensity in said zone, comparing the detected light intensity with one or more threshold values specifically allocated to said zone and which are recorded in memory as being said above parameters, and using the result of this comparison in the determination of the experimental authentication code of the object.