1. A method of authenticating a first document including content and a barcode, said barcode comprising barcode elements each having a predetermined form, said method comprising the steps of: detecting a plurality of the barcode elements of the barcode in a representation of the first document; determining a visual difference between each of the detected barcode elements and the predetermined form of the barcode element; decoding the barcode to determine a second document; and comparing the first document and the second document based on the determined visual difference, in order to authenticate the first document.