A method and arrangement for detecting a watermark embedded in an MPEG compressed signal includes a conventional MPEG decoder stripped to such an extent that a modified baseband video signal suitable for watermark detection is obtained. A plurality of pictures with the embedded watermark is accumulated (2,3,4) in the transform domain, and the inverse DCT (5) is applied to the accumulated result. Conventional watermark detection (6) is then applied to the accumulated plurality of pictures in the spatial domain.