Upscale an image to double with & height, and put a dithering pattern over it.

dither.py

from PIL import Image


def dither(im):
    width, height = im.size
    avg_color = tuple([n / 2 for n in sorted(im.getcolors(width * height))[-1][1]])

    new_im = Image.new("RGBA", (width * 2, height * 2), avg_color)

    for x in xrange(0, width):
        for y in xrange(0, height):
            new_im.putpixel((x * 2, y * 2), im.getpixel((x, y)))

    return new_im


if __name__ == '__main__':
    im = Image.open('unknown.jpg')
    new_im = main(im)
    new_im.save('unknown2.jpg', 'JPEG')