SEO Term Definition
Image Optimisation
Image optimisation is the process of reducing image file size while maintaining visual quality, and adding SEO metadata (alt text, descriptive filenames) so search engines can index images and pages load faster.
Reviewed by Alexander Yarovenko · Updated: 2026-07-03
What is Image Optimisation?
Image optimisation encompasses two distinct aspects of working with images in SEO:
- Technical optimisation — reducing file sizes, using modern formats, and implementing correct loading behaviour to improve page speed and Core Web Vitals
- SEO metadata — adding alt text, descriptive filenames, and structured data so search engines can understand and index images
Technical Image Optimisation
| Optimisation | How to implement | Impact |
|---|---|---|
| Modern formats | Convert JPEG/PNG to WebP or AVIF | 25–50% smaller files |
| Right dimensions | Resize to actual display size (don't serve 4000px image displayed at 400px) | Large file size reduction |
| Compression | Use Squoosh, TinyPNG, or build tools | Further file size reduction |
| Lazy loading | loading="lazy" on <img> tags (not for LCP image) | Faster initial page load |
| Explicit dimensions | Set width and height attributes on all images | Eliminates CLS (layout shift) |
| Priority hint | fetchpriority="high" on the LCP image | Faster LCP |
SEO Metadata for Images
- Alt text — describes the image for screen readers and search engines. Should be descriptive and natural; include the keyword when it's genuinely relevant to the image. Do not keyword-stuff alt text.
- Descriptive filename — "blue-running-shoes.jpg" is better than "IMG_2947.jpg". Use hyphens, not underscores.
- Image sitemap — submit an image sitemap in GSC to help Google discover all images
- Structured data — use ImageObject schema for images that are the primary subject of a page
- Contextual placement — images near relevant text help Google understand what the image depicts