Image optimisation is one of the highest-impact technical SEO improvements you can make to a website. Google uses page speed as a ranking factor, and images are the largest contributor to slow load times. Beyond speed, properly optimised images also appear in Google Image Search — a significant source of traffic that many site owners overlook entirely.
The Four Pillars of Image SEO
Image SEO has four main components: file size (compressed images load faster, improving Core Web Vitals); format (WebP is the recommended format for 2025 — smaller at equal quality); alt text (describes the image to search engines and screen readers); and file name (descriptive filenames help Google understand image content before it even reads the page).
| SEO Factor | Action | Impact |
|---|---|---|
| File size | Compress to <150KB | High — page speed |
| Format | Use WebP | High — 25–35% smaller |
| Alt text | Descriptive keyword text | High — rankings & accessibility |
| File name | Use-keywords-in-filename.jpg | Medium — relevance signal |
| Dimensions | Serve correct size per device | Medium — no wasted bandwidth |
Image SEO Action Plan
- Resize all images to the maximum display width — no larger — using the Image Resizer.
- Compress with the Image Compressor to under 150KB for in-content images.
- Convert to WebP using the Converter.
- Rename files descriptively before uploading —
blue-widget-product-photo.webpnotDSC4521.jpg. - Write alt text for every image in your CMS — describe the image naturally, include the page's primary keyword where it genuinely applies.
Advanced Image SEO
Implement Responsive Images
Use HTML's srcset attribute to serve different image sizes to different screen sizes. Mobile users receive a 400px image; desktop users get the 1200px version. This prevents mobile visitors from downloading unnecessarily large files, directly improving your mobile Core Web Vitals — a significant ranking factor.
Submit an Image Sitemap
An image sitemap helps Google discover and index all the images on your site, including those that might be loaded by JavaScript (which Google sometimes struggles to crawl). WordPress SEO plugins like Yoast and Rank Math include image sitemap generation automatically.
Optimise Your Images for SEO Now
Free, instant, and 100% private — your images never leave your device.
Open Image Compressor →