Grain noise and scratches are applied to an input image as random noise to generate a combined image. When applying grain noise clipped from two-dimensional noise data to the input image, each time clipping is performed, a positional difference from a last clipping position is evaluated. When the positional difference is determined to be small, a current clipping position is changed. When applying scratches clipped from noise data of a plurality of patterns to an input image, when a condition for successively applying scratches for a predetermined time period is selected, a positional difference from a last pasting position is evaluated. When the positional difference is determined to be large, the application of scratches is invalidated.