Redundant coding is a basic method of improving the reliability of detection and survivability after image processing. It embeds watermarks repeatedly in every frame or region and can thus prevent errors due to the accumulation of frames or regions during watermark detection. Redundant coding, however, is not always effective after image processing because the watermark signal may be attenuated by the accumulation procedure when image processing removes watermarks from specific frames or regions. We therefore propose a method of detection to prevent the attenuation of the watermark signal by accumulating a subset of the regions so that the accumulated region has a minimal bit-error rate, which is estimated from the region. Experimental evaluations using actual motion pictures have revealed that the new method can improve watermark survivability after MPEG encoding by an average of 15.7% and can widely be used in correlation-based watermarking.