from PIL import Image
img = Image.open('C:\pics\mona_lisa.jpg')
pix = img.load()
for i in range(img.width):
    for j in range(img.height):
        r, g, b = pix[i, j]
        if r > 50 and g > 50 and b > 50:
            pix[i, j] = (0, 255, 255)
        else:
            pix[i, j] = (255, 0, 255)
img.show()