A method for validating an authentication code enabling an authorised user to access a service or a computer system, the authentication code being a sequence of symbols entered by means of a human-machine interface of a user terminal, comprising the steps of displaying, on a display screen of the user terminal, a digital image of the authentication code entry comprising a plurality of symbols superimposed on a background image, obtaining an authentication code entry by a user by selecting symbols from among the symbols displayed, and of comparing the authentication code entered with a previously saved authentication code, the method being characterised in that it comprises: prior to the step of displaying, steps, implemented by a server adapted to communicate with the user terminal, of: - superimposing graphic elements on the background image at randomly determined positions, each graphic element being representative of a selectable symbol, to form the authentication code entry digital image; - storing, for each graphic element, at least one item of information relating to the symbol represented and to the position of the graphic element in the authentication code entry digital image; and after the step of displaying, steps of: - obtaining (40, 42, 44, 48) a succession of spatial coordinates representative of the successive positions of a point of application moved over the authentication code entry digital image by means of a pointing device, thus forming a continuous trajectory, said trajectory reaching displayed graphic elements, said succession of spatial coordinates forming a list of spatial coordinates representative of points of the trajectory; - determining, by the server, on the basis of said succession of spatial coordinates, a sequence of symbols forming an authentication code. prior to the step of displaying, steps, implemented by a server adapted to communicate with the user terminal, of: - superimposing graphic elements on the background image at randomly determined positions, each graphic element being representative of a selectable symbol, to form the authentication code entry digital image; - storing, for each graphic element, at least one item of information relating to the symbol represented and to the position of the graphic element in the authentication code entry digital image; - superimposing graphic elements on the background image at randomly determined positions, each graphic element being representative of a selectable symbol, to form the authentication code entry digital image; - storing, for each graphic element, at least one item of information relating to the symbol represented and to the position of the graphic element in the authentication code entry digital image; and after the step of displaying, steps of: - obtaining (40, 42, 44, 48) a succession of spatial coordinates representative of the successive positions of a point of application moved over the authentication code entry digital image by means of a pointing device, thus forming a continuous trajectory, said trajectory reaching displayed graphic elements, said succession of spatial coordinates forming a list of spatial coordinates representative of points of the trajectory; - determining, by the server, on the basis of said succession of spatial coordinates, a sequence of symbols forming an authentication code. - obtaining (40, 42, 44, 48) a succession of spatial coordinates representative of the successive positions of a point of application moved over the authentication code entry digital image by means of a pointing device, thus forming a continuous trajectory, said trajectory reaching displayed graphic elements, said succession of spatial coordinates forming a list of spatial coordinates representative of points of the trajectory; - determining, by the server, on the basis of said succession of spatial coordinates, a sequence of symbols forming an authentication code.