Outline text on image in Python

I don't know since what version, but about a year ago Pillow added text stroking. You probably need to update it if you haven't do so lately. Example usage with stroke_width of 2:

from PIL import Image, ImageDraw, ImageFont

caption = 'I need to update my Pillow'
img = Image.open('./example-img.jpg')
d = ImageDraw.Draw(img)
font = ImageFont.truetype('impact.ttf', size=50)
d.text((10, 400), caption, fill='white', font=font,
       stroke_width=2, stroke_fill='black')
img.save('example-output.jpg')

You can use mathlibplot text Stroke effect which uses PIL.

Example:

import matplotlib.pyplot as plt
import matplotlib.patheffects as path_effects
import matplotlib.image as mpimg

fig = plt.figure(figsize=(7, 5))
fig.figimage(mpimg.imread('seal.jpg'))
text = fig.text(0.5, 0.1, 'This text stands out because of\n'
                          'its black border.', color='white',
                          ha='center', va='center', size=30)
text.set_path_effects([path_effects.Stroke(linewidth=3, foreground='black'),
                       path_effects.Normal()])
plt.savefig('meme.png')

Result: