pip install pillow~=10.3

from PIL import Image, ImageDraw

# https://en.wikipedia.org/wiki/Envelope_%28mathematics%29

dim = 200  # Image dimensions (pixels)
skip = 10   # Only draw a line every X pixels
width = 1   # Line width
color = "white"

with Image.new(mode = "RGB", size = (dim, dim)) as im:  # mode="RGBA" for transparent background
    draw = ImageDraw.Draw(im)

    for i in range(dim):
        if i % skip:
            continue
        rev = dim - i
        draw.line([(0, i), (i, dim)], fill=color, width=width) 

    im.show()  # im.save("/tmp/Envelope.png")