1. An image processing device comprising: a pixel value determining section which determines pixel values of background pixels based on a pixel value histogram of a target image to be segmented into a foreground and a background; a first determination section which determines pixels of the target image having pixel values equivalent to the pixel values of the background pixels, as a portion of the background pixels; and a second determination section which determines other background pixels and foreground pixels in the target image by use of a pixel value of each pixel in the target image and positional information of the portion of the background pixels.