Adds a border to image files ready for uploading to Instagram. Required Python Pillow/PIL library to be installed. Output image size, border size, and image size as proportion of output are hardcoded - alter according to your needs!

add_border.py

"""Adds a border to image files ready for uploading to Instagram."""

import os
import sys

from PIL import Image, ImageDraw

# output image and border sizes in pixels
WIDTH = HEIGHT = 3000
BORDER = 0
# original image size as proportion of output size
IMG_PROP = 0.9


def main(args):
    if not args:
        print('Usage: add_border.py <path to image>')
        return
    for in_path in args:
        fname, ext = os.path.splitext(in_path)
        if fname.endswith('_border'):
            print(f"Skipping {in_path}")
            continue
        with Image.open(in_path) as img:
            width, height = img.size
            ratio = WIDTH / max(width, height)
            new_width = int(round(IMG_PROP * ratio * width))
            new_height = int(round(IMG_PROP * ratio * height))
            img_x = int(round((WIDTH / 2) - (new_width / 2)))
            img_y = int(round((WIDTH / 2) - (new_height / 2)))
            new_img = Image.new("RGB", (WIDTH, HEIGHT), (255,255,255))
            if BORDER:
                border_width = new_width + BORDER * 2
                border_height = new_height + BORDER * 2
                bx0 = int(round((WIDTH / 2) - (border_width / 2)))
                by0 = int(round((WIDTH / 2) - (border_height / 2)))
                bx1 = int(round((WIDTH / 2) + (border_width / 2)))
                by1 = int(round((WIDTH / 2) + (border_height / 2)))
    
                d = ImageDraw.Draw(new_img)
                d.rectangle([(bx0, by0), (bx1, by1)], fill='black', outline='black')
                
            img_resized = img.resize((new_width, new_height))
            new_img.paste(img_resized, box=(img_x, img_y))
            out_path = f'{fname}_border{ext}'
            new_img.save(out_path)


if __name__ == '__main__':
    main(sys.argv[1:])