Images are central to SEO in two ways: they drive image search traffic on their own, and they directly affect Core Web Vitals (LCP, CLS) that feed Google's ranking. Bad images can drag an otherwise great page down. Here's the practical checklist that actually moves the needle in 2026.
1. Shrink files (the LCP lever)
The Largest Contentful Paint is very often a hero image. If that image is 2 MB, your LCP is doomed. Compress the hero to under 150 KB (ideally under 100 KB) using AVIF or WebP. Use Kix Image Tools to get there — see reduce image size without losing quality.
2. Use modern formats
Serve AVIF (or WebP) with a JPEG fallback via the <picture> element. Modern formats cut bytes 30–50% versus JPEG at equal quality, directly improving LCP.
3. Set width and height (the CLS lever)
Always specify width and height on <img>. The browser reserves space before the image loads, preventing Cumulative Layout Shift. CLS is a Core Web Vital — layout jumps hurt ranking and UX.
4. Lazy-load below the fold
Add loading="lazy" and decoding="async" to images below the first viewport. This delays their fetch, speeding up initial render. But do not lazy-load the LCP image — that delays it.
srcset lets mobile devices download a small version and desktops a large one — huge for mobile LCP.5. Write real alt text
alt text is the single biggest image SEO signal: it's how Google understands the image and how screen readers describe it. Write descriptive, keyword-natural text — not stuffed keywords, not "image123". For purely decorative images, use empty alt="".
6. Use descriptive filenames
red-running-shoes-nike.jpg beats IMG_4823.jpg. Filenames are a minor but real ranking signal in image search. Compress first, rename, then upload.
7. Add structured data where relevant
For product images, recipes, and articles, JSON-LD with image properties helps Google rich results. Make sure the referenced image URL is the compressed, final one.
8. Use a content delivery network (CDN)
A CDN caches compressed images close to users, cutting TTFB and download time. Combine with the right Cache-Control headers (long max-age, immutable) so returning visitors pay nothing.
The 2026 image SEO checklist
- Hero image under 150 KB, AVIF/WebP
width/heighton every<img>- Lazy-load below the fold, not the LCP
- Descriptive
altand filename on every meaningful image - Responsive
srcsetfor mobile/desktop - Long cache headers + CDN
Summary
Image SEO is mostly mechanical: compress, set dimensions, write real alt text, lazy-load sensibly. Kix Image Tools handles the compression half — the rest is on your markup.