from PIL import Image
import os

ss_dir = r'C:\UT2004\ScreenShots\\'
dest_dir = r'C:\UT2004\ScreenShots\Upload\\'
final_size = (1024,768)

filenames = os.walk(ss_dir)
filenames = list(filenames)[0][2]
for i in [j[:-4] for j in filenames if j.endswith('.bmp')]:
    im = Image.open(ss_dir+i+'.bmp')
    im = im.resize(final_size)
    im.save(dest_dir+i+'.jpg')