A method of controlling access to a resource using a verifying device uses watermarking device that embeds an authorization code in a signal using watermarking technology. The watermarked signal is then transmitted to a verifying device, e.g. as a television or radio program or as a commercial related to the resource. In the verifying device, the authorization code is extracted from the watermarked signal and an operation to be performed on the resource is authorized in dependence on the extracted authorization code. Preferably the authorization includes permission for executing a program, rendering and/or copying a multimedia object or for activating a cheat function in an electronic game.