1. An image data processing method including: a motion data computation process for calculating the motion data between a reference image and a target image; a block comparison process for adjusting displacement between the reference image and the target image by using the motion data, dividing the reference image and the target image into blocks, and calculating difference in pixel value between the reference image and the target image for every block; a blending ratio calculation process for calculating, based on the difference in pixel value, the blending ratio between the reference image and the target image for each block; an image synthesizing process for creating a synthesized image by synthesizing the reference image and the target image according to the motion data and the blending ratio; and a noise reduction process for applying a noise reduction filter in the obtained synthesized image so as to change the coefficient for every block depending on the number of images synthesized together; wherein, when the difference in the pixel value exceeds a predetermined threshold, the blending ratio is set to 0; whereby prevents a photographic subject from becoming indistinct even if there is a moving subject in a captured image and obtains a blur-compensated image.