An authentication system, comprising - a data terminal with a data terminal device, - a communication network - an authentication service, wherein the authentication service comprises a database, in which user reference data is stored, and - a point of sale; - wherein the data terminal device comprises an image capturing device, an image editing module and a wireless communication interface, - wherein, via the communication network, a first communication connection is established between the data terminal device and the authentication service; wherein - the data terminal is formed by a watch, - wherein the data terminal is arranged in an independent housing, - wherein the authentication service has a face detection and face recognition module and, moreover, a 2D/3D image analysis module, which 2D/3D image analysis module is configured for recognizing a real person as a 3D object in a picture captured by the image capturing device and transmitted via the first communication connection, by comparing a result of the picture analysis of the picture captured by the image capturing device and transmitted via the first communication connection to the user reference data stored in the database; - wherein the wireless communication interface is configured as a far range interface and as a close range interface, - wherein the close range interface of the wireless communication interface is configured to be unidirectional, - wherein, at the point of sale, an authentication prompt is triggered by the data terminal device, and, by means of the wireless communication interface configured as a close range interface, a short-range data connection is established with a corresponding remote station of the point of sale, wherein the wireless communication interface of the data terminal is configured such that it detects an unambiguous identifier from the point of sale via the short-range data connection, and is configured such that it transmits said univocal identifier to the authentication service via the first communication connection of the communication network; - wherein the authentication service further comprises an interface, and that an additional communication connection is established, via the communication network, between the point of sale and the interface of the authentication service,; and wherein the face detection and face recognition module is configured such that in case of an accordance between the result of the image analysis and the user reference data, it transmits the univocal identifier, as an authentication signal, to the point of sale via the additional communication connection of the communication network. - a data terminal with a data terminal device, - a communication network - an authentication service, wherein the authentication service comprises a database, in which user reference data is stored, and - a point of sale; - wherein the data terminal device comprises an image capturing device, an image editing module and a wireless communication interface, - wherein, via the communication network, a first communication connection is established between the data terminal device and the authentication service; - the data terminal is formed by a watch, - wherein the data terminal is arranged in an independent housing, - wherein the authentication service has a face detection and face recognition module and, moreover, a 2D/3D image analysis module, which 2D/3D image analysis module is configured for recognizing a real person as a 3D object in a picture captured by the image capturing device and transmitted via the first communication connection, by comparing a result of the picture analysis of the picture captured by the image capturing device and transmitted via the first communication connection to the user reference data stored in the database; - wherein the wireless communication interface is configured as a far range interface and as a close range interface, - wherein the close range interface of the wireless communication interface is configured to be unidirectional, - wherein, at the point of sale, an authentication prompt is triggered by the data terminal device, and, by means of the wireless communication interface configured as a close range interface, a short-range data connection is established with a corresponding remote station of the point of sale, wherein the wireless communication interface of the data terminal is configured such that it detects an unambiguous identifier from the point of sale via the short-range data connection, and is configured such that it transmits said univocal identifier to the authentication service via the first communication connection of the communication network; - wherein the authentication service further comprises an interface, and that an additional communication connection is established, via the communication network, between the point of sale and the interface of the authentication service,; and