This is a very simple image resizer that keeps the aspect ratio.

resizer.py

import os, sys
from PIL import Image



def rezise(dir, size: tuple = (768, 512)) -> None:
    for infile in os.listdir(dir):
        outfile = os.path.splitext(infile)[0] + "_resized.thumbnail"
        if infile != outfile:
            try:
                with Image.open(os.path.join(dir, infile)) as im:
                    cp = im.copy()
                    cp.thumbnail(size, Image.ANTIALIAS)
                    cp.save(os.path.join(dir, outfile), "JPEG")
                    print("Resized: " + infile)


        except IOError:
            print("Cannot resize " + infile)