Image Automation with Python: Batch Resize, Compress and Watermark

Hong Kong SMEs running an online shop, Facebook or Instagram deal with piles of product photos every day: websites demand images that aren't too large (or pages load slowly and eat customers' mobile data), social media wants specific dimensions, and you still need a watermark to protect your originals. Resizing, compressing and watermarking each one by hand is fine for eight or ten — but a hundred?

This tutorial uses Python with a library called Pillow to process an entire folder of photos in a dozen lines of code. Even if you've never written code before, you can follow along.

Step 1: Install Pillow

First make sure Python is installed (if not, see our earlier beginner tutorial). Then open Command Prompt and install Pillow with:

pip install Pillow

When you see Successfully installed Pillow, you're ready.

Step 2: What does the script do?

This script does three things for you in one go:

Resize — shrinks anything wider than 1200 pixels (never upscales, so quality stays intact)
Compress — converts to JPEG and lowers quality, shrinking files dramatically so your site loads fast
Watermark — adds a line of text to the bottom-right corner to deter image theft

Step 3: Write the script

Create a new file called resize.py (Notepad is fine) and paste in the code below:

from PIL import Image, ImageDraw, ImageFont
from pathlib import Path

SRC = Path("photos")          # Put your originals here
OUT = Path("resized")         # Output folder
OUT.mkdir(exist_ok=True)

MAX_W = 1200                  # Max width in pixels
QUALITY = 80                  # JPEG quality (lower = smaller file)
WATERMARK = "Sky World Biz"

n = 0
for p in SRC.glob("*"):
    if p.suffix.lower() not in (".jpg", ".jpeg", ".png"):
        continue

    img = Image.open(p).convert("RGB")

    # 1) Resize: only shrink, never enlarge
    w, h = img.size
    if w > MAX_W:
        img = img.resize((MAX_W, int(h * MAX_W / w)))

    # 2) Add a watermark to the bottom-right corner
    draw = ImageDraw.Draw(img)
    font = ImageFont.load_default()
    bbox = draw.textbbox((0, 0), WATERMARK, font=font)
    tw, th = bbox[2] - bbox[0], bbox[3] - bbox[1]
    draw.text((img.width - tw - 10, img.height - th - 10),
              WATERMARK, fill=(255, 255, 255), font=font)

    # 3) Compress and save
    img.save(OUT / (p.stem + ".jpg"), "JPEG",
             quality=QUALITY, optimize=True)
    n += 1

print("Done! Processed", n, "photos")

Line by line

from PIL import Image, ImageDraw, ImageFont — loads Pillow's three core tools: opening images, drawing, and fonts.
SRC = Path("photos") — the source folder; put your photos here.
MAX_W = 1200 — the width cap. 1200px is plenty for web and social media.
QUALITY = 80 — JPEG quality from 1 (smallest) to 100 (sharpest). 80 is usually indistinguishable to the eye but far smaller.
SRC.glob("*") — lists every file in the folder, then p.suffix checks whether it's an image.
img.resize((MAX_W, int(h * MAX_W / w))) — shrinks proportionally so the aspect ratio never distorts.
draw.text(...) — draws the watermark bottom-right; the -10 leaves a 10-pixel margin.
img.save(..., quality=80, optimize=True) — saves compressed, and optimize squeezes the file a little more.

Step 4: Run it

In Command Prompt, navigate to where you saved resize.py and run:

python resize.py

Done! The resized folder now holds your processed photos, and your originals are untouched.

How to pick the quality setting

The QUALITY number is a balance between sharpness and file size. As a rule of thumb:

90–100 — near-lossless; for photos you may print large
75–85 — product and social-media images; visually identical but 60–70% smaller
50–70 — thumbnails or previews only, not for display

Summary

Python Tutorial: With a dozen lines of code you've handed the repetitive resize-compress-watermark grunt work to the computer, freeing up time to focus on your business. Using the same idea, you can add automatic borders, batch format conversion — or combine it with our earlier scheduling tutorial to make it run every day on its own.