cats

from PIL import Image

n = 3
cat = Image.open('cat.jpg')
width, height = cat.size
cats = Image.new('RGB', (width*(2*n - 1), height*n), color=(255, 255, 255))

for i in range(n):
    for j in range(2*i + 1):
        cats.paste(cat, ((n - i + j - 1)*width, i*height))

cats.save('cats.jpg')