Join the list of images into the out file

def join_images(img_files, out_file):
    """Join the list of images into the out file"""
    images = [PIL.Image.open(f) for f in img_files]
    joined = PIL.Image.new(
        'RGB',
        (sum(i.size[0] for i in images), max(i.size[1] for i in images))
    )
    left = 0
    for img in images:
        joined.paste(im=img, box=(left, 0))
        left = left + img.size[0]
    joined.save(out_file)