Here is an example from PILs docs:

from PIL import Image
import glob, os

size = 128, 128

for infile in glob.glob("*.jpg"):
    file, ext = os.path.splitext(infile)
    with Image.open(infile) as im:
        im.thumbnail(size)
        im.save(file + ".thumbnail", "JPEG")

The docs are here:

https://pillow.readthedocs.io/en/stable/index.html

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