make_collage.py

import os

from PIL import Image

image_fs = os.listdir()
image_fs.sort()
image_fs = image_fs[:9]
images = map(Image.open, image_fs)
(widths, heights) = zip(*(i.size for i in images))

col_width = min(widths)
row_height = min(heights)

(num_rows, num_cols) = (3, 3)
new_im = Image.new("RGB", (num_cols * col_width, num_rows * row_height))

for (i, image_f) in enumerate(image_fs):
    image = Image.open(image_f).resize((col_width, row_height)).rotate(-90)
    x_offset = (i % num_cols) * col_width
    y_offset = (i // num_cols) * row_height
    new_im.paste(image, (x_offset, y_offset))

new_im.save("out.pdf")