Transaction system

Associating a transaction identifier with a payment means involves a method of registering a transaction identifier which uses a portable device 12, such as a tablet or mobile phone. The device comprises an input mechanism arranged to enable input of an identifier, i.e. face or car registration number 18, and a selection mechanism arranged to enable the user to select a payment mechanism, such as a card in an electronic wallet, to be associated with the identifier. The portable device further comprises a communication module arranged to transmit data relating to the identifier and the payment mechanism selection to a remote payment server 14. The input mechanism may be a camera or a touch screen and the device may include facial or number plate recognition software. During a transaction, for example at a toll gate, congestion charging zone, car park, or petrol station an image of the identifier (car number plate or face) is recognized and a request for payment is made by the operator server to the payment server. The transaction may be automatically settled by the payment server or verification and authentication via the user mobile device may be requested.