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optimize_images.py

Standalone script: pass it one or more image URLs (e.g. ones PageSpeed Insights flags as oversized) and it downloads + re-saves each as optimized JPEG and WebP, organized into original//jpg//webp/ folders.

It doesn't resize — only recompresses/reformats — so the output is safe to reuse anywhere the original was used (mobile, desktop, any breakpoint).

Requirements​

pip3 install --user Pillow

Usage​

python3 optimize_images.py --output findings/image-optimization \
    https://their-domain.org/wp-content/uploads/2024/big-photo.png \
    https://their-domain.org/wp-content/uploads/2024/other.jpg

Behavior​

  • Detects real alpha-channel transparency before converting — if an image genuinely uses transparency, it's left alone (converting to JPEG would silently destroy it) rather than corrupting the output.
  • Reports a before/after size summary, including total savings across all images passed in.
  • Typical results: 80-95% smaller file size at the same visual quality, since most flagged images are unnecessarily large PNGs where a JPEG or WebP re-encode loses nothing visible.

Handoff tip​

Lead with the .webp folder when handing files to a non-technical org — it's the smallest and supported by every modern browser. Keep .jpg as the fallback only if they have a specific reason to need it.