Abstract: A steganographic method is presented that provides authentication of user identity, such that only an authorized user may reveal the data hidden steganographically. Two data objects such as images are used for this purpose, one hidden within the other. A key provision of the invention allows the ‘inner’ image to itself contain hidden data that is not corrupted by subsequent compression within the ‘outer’ image. A digital ‘scratch card’ is by this means implemented, where the inner image is only revealed to an authorized user. Using this algorithm, physical cards containing data are represented by a single digital object.