Authentication device comprising - a security element with at least one security feature consisting of characters which can be detected via character recognition, wherein the security element has at least one structural feature which influences the appearance of the security feature and thus the detectability of one or more characters of the security feature during character recognition and/or character interpretation, - at least one detection device for detecting the appearance of the characters of the security feature, - at least one optical character recognition device for carrying out optical character recognition in which the recognizable characters of the appearance of the security feature are converted into machine-readable characters, wherein one or more characters of the security element are manipulated in such a way that, in an OCR recognition or OCR analysis, characters that are difficult or impossible to read are interpreted differently or are reassigned according to a rule, - at least one comparison device for comparing the security feature detected by the detection device and/or the characters, converted by the character recognition device with a reference feature stored in a memory, characterized in that the authentication device comprises at least one control device, which prescribes the rules and/or parameters for the detection and/or reading and/or analysis for the characters of the security feature in such a way that the detection conditions for detecting the appearance of the characters and/or the reading conditions for the character recognition and/or the analysis parameters for the character analysis of the characters of the security feature are specified for an authentication request of the control device are changed in an unpredictable way by the selection of the parameters being predetermined by the authentication device or being random. - a security element with at least one security feature consisting of characters which can be detected via character recognition, wherein the security element has at least one structural feature which influences the appearance of the security feature and thus the detectability of one or more characters of the security feature during character recognition and/or character interpretation, - at least one detection device for detecting the appearance of the characters of the security feature, - at least one optical character recognition device for carrying out optical character recognition in which the recognizable characters of the appearance of the security feature are converted into machine-readable characters, wherein one or more characters of the security element are manipulated in such a way that, in an OCR recognition or OCR analysis, characters that are difficult or impossible to read are interpreted differently or are reassigned according to a rule, - at least one comparison device for comparing the security feature detected by the detection device and/or the characters, converted by the character recognition device with a reference feature stored in a memory, characterized in that the authentication device comprises at least one control device, which prescribes the rules and/or parameters for the detection and/or reading and/or analysis for the characters of the security feature in such a way that the detection conditions for detecting the appearance of the characters and/or the reading conditions for the character recognition and/or the analysis parameters for the character analysis of the characters of the security feature are specified for an authentication request of the control device are changed in an unpredictable way by the selection of the parameters being predetermined by the authentication device or being random.