Monitoring

Image Optimisation Checks

Identify oversized, unoptimised, and poorly formatted images on your site.

Updated 2026-03-17

2 min read

images

optimization

webp

Image Optimisation Checks#

Images are typically the largest assets on a web page. LemWatch scans your pages and identifies optimisation opportunities.

Check	Description
Oversized images	Images served at dimensions much larger than displayed
Unoptimised formats	Images using PNG/JPEG when WebP or AVIF would be smaller
Missing dimensions	Images without width/height attributes (causes layout shift)
Total page weight	Combined size of all images on the page
Lazy loading	Whether off-screen images use `loading="lazy"`

For each page checked, you'll see:

Total images found on the page

Oversized count — Images that could be resized

Unoptimised format count — Images not using modern formats

Total size in KB and potential savings in KB

Per-image details — URL, current format, dimensions, and recommended changes

LemWatch provides actionable recommendations:

Convert to WebP/AVIF — Modern formats are 30–50% smaller

Resize to display dimensions — Don't serve 4000px images in 400px containers

Add width and height — Prevents Cumulative Layout Shift (CLS)

Enable lazy loading — Defer off-screen images

Use a CDN with auto-optimisation — Cloudflare, Imgix, or Cloudinary

LCP — Large unoptimised hero images directly increase Largest Contentful Paint

CLS — Missing dimensions cause layout shifts as images load

INP — Heavy images can block the main thread during decode

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