TRANSACTION PROCESSING SYSTEM

A transaction processing system comprises at least one transaction terminal (10, 11, 12) having means to receive characteristic data from a user, which characteristic data is required to generate a characteristic image associated with the user, such as an image of the user's signature, from data stored in a data processing system (14); and logic for generating a transaction message by combining transaction data with the characteristic data in such a way that the transaction data is required to recover the characteristic data from the message. The data processing system (14) comprises means to store the user data, to receive and store the message, to recover the characteristic data from the message using the transaction data, and to reconstruct the characteristic image from the user data using the characteristic data to establish that the transaction was valid by associating the characteristic image with the transaction data.