The image is mixed 2 pictures. The darker one has the answer.
The following code is for the one which has answer. The other picture was produced by the code just switching the arguments of the 2 getpixel sentences.
import Image, ImageDraw im = Image.open('cave.jpg') draw = ImageDraw.Draw(im) for j in range(im.size / 2): for i in range(im.size - 2): if i % 2 == 0: im.putpixel((i, j), im.getpixel((i, j*2))) else: im.putpixel((i, j), im.getpixel(i, j*2 + 1)) im.save('cave3.jpg')