Images are the SEO layer almost every site treats as an afterthought. That's where the easy wins live. Good image SEO drives image-search traffic, improves Core Web Vitals, helps accessibility, and adds topical context to your page. This page walks through the seven-point image checklist every image on your site should pass, the formats that actually matter in 2026, and the lazy-load and sizing rules that keep Google happy.
Four jobs at once. First, Google Images sends real traffic on certain queries. Recipes, products, how-to steps. Second, images are a major Core Web Vitals variable. Badly-served images torpedo LCP. Third, alt text is accessibility. Fourth, images contribute to the on-page topical signal.
A page that treats images well gets all four benefits for the same work. A page that treats images as decoration loses on all four.
Rename files before uploading. Use descriptive, hyphenated names. The file name is a small relevance signal Google reads.
IMG_4827.jpgscreen-shot-2026-04-18-at-1142am.pnginsurance-crm-dashboard.jpgThe alt attribute describes the image for screen readers and search engines. Write actual descriptions, not keyword lists.
If the primary keyword fits naturally in the alt text, include it. If it doesn't, don't force it. Decorative images (gradients, flourishes) should use alt="", not omit the attribute.
Format matters a lot for page speed.
Every image should be compressed before upload. Target under 200KB for photos, under 100KB for illustrations. Anything over 500KB needs a good reason to exist.
Free tools: Squoosh (browser-based, uses Google's compressors), TinyPNG, ImageOptim. Any CMS or hosting platform worth its salt has automated pipelines for this now.
Don't serve a 4,000px image into an 800px slot. Use srcset to serve correctly-sized images per device.
<img src="hero.jpg"
srcset="hero-400.jpg 400w, hero-800.jpg 800w, hero-1600.jpg 1600w"
sizes="(max-width: 800px) 100vw, 800px"
alt="...">The browser picks the best size for the user's device. Mobile users save bandwidth. Desktop users get crisp images. Everyone wins.
Images below the fold should lazy-load. Native HTML support is universal now:
<img src="..." loading="lazy" alt="...">Don't lazy-load the hero image or anything that's visible when the page first loads. Lazy-loading above-the-fold hurts LCP, which hurts rankings.
Always set explicit width and height attributes. This reserves space for the image before it loads, preventing layout shifts. Your CLS score stays clean.
<img src="..." width="800" height="600" alt="...">Studies have shown captions are the highest-read text on a page. Readers scan them before body text. Treat captions as real content. They also pass relevance signals.
For images that belong to a schema object (Product, Recipe, Article), include them in the structured data. It qualifies your images for rich image-search results.
Google's image sitemap spec lets you list every image on your site separately. For image-heavy sites (photography, ecommerce, recipe sites), it's worth setting up. For typical content sites, your main XML sitemap with inline image references is enough.
Audit your top 20 pages. For each, check the images against the 7-point checklist. Most sites fail 3 to 5 points per image. Fix the biggest wins first: compression and alt text. You'll see Core Web Vitals improve in weeks and image-search traffic trickle in over months.
Next: schema markup, the structured-data layer that unlocks rich SERP results.