A method, device and arrangement insert extra information in an input signal in the acoustical or visual domain. A representation in the electrical domain is received, a watermark including the extra information is generated, and a watermark signal representing the watermark is output to the acoustical or visual domain. The watermark signal representing the watermark is merged with the input signal in the acoustical or visual domain. Any recording unit which attempts to record the input signal will automatically record the watermark signal as well, so no unwatermarked specimens are made available. The device may be realized as a computer program product, or as a small portable unit, which may be worn by a person to automatically watermark anything spoken. The device may be used to protect physical objects against unauthorized taking of photographs, by projecting a visual watermark signal towards the source or physical object.