resize_photos.py

import os, sys
import Image

sizes = [100, 200, 300]

def read_directory(path, new_path):
    # create new directories to store resized photos
    for size in sizes:
        size_dir = new_path+'_'+str(size)
        if not os.path.exists(size_dir):
            os.makedirs(size_dir)
    for dirname, dirs, files in os.walk(path):
        for infile in files:
            for size in sizes:
                outfile = os.path.join(new_path+'_'+str(size), infile)
                infile_full = os.path.join(path, infile)
                resize_photo(infile_full, outfile, size)

def resize_photo(original_photo, new_photo, size):
    try:
        photo = Image.open(original_photo)
        photo.thumbnail((size,size), Image.ANTIALIAS)
        photo.save(new_photo, "JPEG")
    except IOError:
        print "cannot create thumbnail for '%s'" % original_photo

#final 'photos' will be appended with _size for each size needed
read_directory('/path/to/photos/dir', '/path/to/resized_photos/dir/photos')