Image data generated at a first mobile device is transferred to a storage service that is accessible via a communications infrastructure and with which a first party associated with the first mobile entity is preferably registered. This transfer is effected via one or more nearby third-party mobile devices with the first mobile device initially transferring the image data and an identifier of itself to the or each nearby third-party mobile device by using, for example, a short-range wireless link. The or each third-party device is then responsible for directly or indirectly forwarding the image data and the first-party identifier over the communications infrastructure to the storage service where it is stored. In one preferred embodiment, a reward is credited to any party whose device has been used in the successful transfer of image data to the storage service on behalf of the first party.