Images are usually the heaviest thing on a web page, which makes them one of the biggest levers on your SEO. They affect rankings in three ways: page speed and Core Web Vitals, image search visibility, and on-page relevance. Here is how to optimise for all three.
1. Speed: the ranking factor you can feel
Google uses Core Web Vitals as a ranking signal, and images directly drive Largest Contentful Paint (LCP) — usually the biggest image above the fold. Shrink it and your LCP improves. The essentials:
- Serve modern formats (WebP/AVIF) instead of JPG/PNG.
- Resize images to the dimensions they are actually displayed at.
- Compress to quality ~80.
- Specify
widthandheightso the layout doesn't shift (protecting your CLS score).
2. Lazy loading and responsive images
Add loading="lazy" to below-the-fold images so the browser only
loads them when needed. Use srcset to serve smaller images to phones and
larger ones to desktops. Together these cut the initial page weight substantially.
3. Alt text and file names
Descriptive alt text helps accessibility and tells search
engines what the image shows — it is how you rank in Google Images. Write natural,
specific descriptions ("golden retriever puppy on a beach"), not keyword stuffing.
Give files meaningful names (red-leather-handbag.webp, not
IMG_4821.webp).
4. Structured data and sitemaps
Where relevant, mark up images with structured data (product, recipe, article) so they can appear as rich results. Make sure important images are reachable in your sitemap so they get indexed.
5. The prioritised checklist
- Convert to WebP/AVIF.
- Resize to display size.
- Compress to ~80 quality.
- Set explicit width/height.
- Lazy-load below-the-fold images.
- Write descriptive alt text and file names.
Do those six things and your images will stop dragging your rankings down and start helping them.