A method and apparatus are provided for the secure provision of payload data that comprises image data representing an image. The payload data is encrypted using encryption parameters comprising public data of a trusted party and an encryption key string. The encryption key string comprises thumbnail data that represents a low-resolution version of the image represented by the image data. The encryption key string preferably also comprises at least one condition to be met before the trusted party releases a decryption key for decrypting the encrypted payload data; advantageously, the apparatus enables a user to select, via a user interface, one or more conditions for incorporation into the encryption key string. The functionality for generating the thumbnail data, for choosing the conditions to be used for the encryption key string, and for encrypting the payload data is preferably incorporated into a physical add-in module such as a PCMCIA card.