Image SEO: filenames, sizes, formats, and lazy loading done right
Beyond alt text, four image attributes matter for SEO and speed: descriptive filenames, modern formats (WebP/AVIF), explicit width/height, and lazy loading for below-the-fold images.
Beyond alt text, four image attributes matter for SEO and speed: descriptive filenames, modern formats (WebP/AVIF), explicit width/height, and lazy loading for below-the-fold images. Image SEO covers filename hygiene (descriptive, lowercase, hyphenated), file format (WebP/AVIF over JPG/PNG when possible), dimensions in HTML (prevents layout shift), loading="lazy" (defers off-screen images), and reasonable compression (~150KB or less for hero images).
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What it is
Image SEO covers filename hygiene (descriptive, lowercase, hyphenated), file format (WebP/AVIF over JPG/PNG when possible), dimensions in HTML (prevents layout shift), loading="lazy" (defers off-screen images), and reasonable compression (~150KB or less for hero images).
Why it matters
Google Images is a substantial source of long-tail traffic — especially for product, recipe, and visual content. Slow or unoptimised images also dominate LCP scores. AI engines also extract image filenames and surrounding text as context for the page.
How to fix it
- Rename image files descriptively. IMG_4831.jpg → red-leather-armchair-eames-style.jpg before upload. Lowercase, hyphenated, no spaces.
- Convert to WebP or AVIF. WebP at quality 80 is typically 25–35% smaller than equivalent JPG. AVIF goes further but with slower encode.
- Set explicit width and height attributes. <img width="800" height="600"> reserves space and eliminates layout shift while the image loads.
- Lazy-load below-the-fold images. Add loading="lazy" to images below the initial viewport. Never lazy-load LCP images.
Authoritative sources
- Google Search Central documentation — Google
- Schema.org vocabulary — schema.org
- SEO Starter Guide — Google Search Central
- MDN — HTML meta and link elements — Mozilla MDN