1. An image processing device comprising: processing circuitry including a processor and a memory encoded with instructions configured to: detect, from a criteria image and a reference image, a motion vector of each block in an image; generate a motion-compensated image by performing motion compensation on the reference image, using the motion vector; calculate a correction value for correcting a pixel value of a current pixel in a current block in the motion-compensated image based on a boundary difference value between the criteria image and the motion-compensated image, the boundary difference value being a difference value that is determined with respect to a pixel value of a boundary pixel in a boundary portion adjacent to an adjacent block in the current block; add the correction value to the pixel value of the current pixel in the motion-compensated image; approximate a difference value with a predetermined function, the difference value being a difference between a pixel value of a pixel in the criteria image and a pixel value of a pixel in the motion-compensated image on a block-by-block basis; integrate the predetermined function; calculate a weight coefficient in accordance with a value of an integral obtained by integrating the predetermined function and a distribution of noise intensity corresponding to an image luminance value; and weight the correction value for the current pixel by using the weight coefficient, wherein the weighted correction value is added to the pixel value of the current pixel in the motion-compensated image.