Mark images with proportional text

markImages.py

from PIL import Image, ImageDraw, ImageFont
import os

filelist = os.listdir(".")
filelist.sort()

jpglist = []
for filename in filelist:
    if filename[0] == "g":
        jpglist.append(filename)

for filename in jpglist:
    im = Image.open(filename)
    width, height = im.size
    size = int(0.05 * min(width, height))
    draw = ImageDraw.Draw(im)
    draw.rectangle((0, height - size, size * 6, height), fill="white")
    font = ImageFont.truetype("arial.ttf", size)
    draw.text((size * 3, height - size / 2), "0.5cm grid", fill="black", anchor="mm", font=font)
    im.save("out" + filename)