Image SEO

Long definition

Image search drives meaningful traffic to retail, recipe, travel, and visual-product verticals — Wirecutter, Bon Appétit, Etsy all see double-digit percentages of organic sessions originate in Image Search. The optimization layer is small but most sites skip half of it.

Filename. Descriptive, kebab-case, short. red-leather-jacket-women-medium.jpg beats IMG_4583.jpg. Filenames are a weak signal individually but compound across a site of thousands of images.

Alt text. The single most important image-SEO field — see alt-text for the full breakdown. Describe what the image actually shows in 8-15 words; don't keyword-stuff; leave decorative images with alt="".

Dimensions and format. Serve images at the size the layout uses. A 4000×3000 source rendered into a 400×300 thumbnail wastes 99% of the bytes. Format priority: AVIF (best compression, supported in all modern browsers since 2023), WebP (universal fallback), JPEG/PNG (legacy fallback). web.dev's image guide covers the encoding decisions.

Responsive srcset and sizes. Serve different image dimensions to different viewports via <img srcset="small.webp 480w, medium.webp 800w, large.webp 1200w" sizes="(max-width: 600px) 480px, 100vw">. The browser picks the right one based on viewport and DPR. Without srcset, mobile users download desktop-sized images, killing LCP.

loading="lazy". Native lazy loading on every below-the-fold image. Don't lazy-load the LCP image — it delays the load instead of helping it. Above-the-fold heroes get loading="eager" and fetchpriority="high".

Width and height attributes. Always set width and height (or aspect-ratio in CSS). Without them, the browser doesn't know how much space to reserve and you get layout shift — a CLS regression that quality systems read as a poor experience signal.

Image sitemap. Either a dedicated image sitemap or <image:image> extensions inside the regular XML sitemap. Tells Google which images on each page deserve indexing — particularly useful for sites where images are loaded by JavaScript or behind interactions.

Common misconceptions

• "Alt text should match a target keyword." Alt describes the image. If the image is a red leather jacket, "red leather jacket on white background" is the alt — not "buy cheap leather jackets online". Stuffing breaks accessibility and triggers spam patterns.
• "WebP is enough." AVIF beats WebP by 20-30% on the same quality. Modern stacks serve AVIF with WebP fallback and JPEG as final fallback.
• "Lazy load everything." The hero/LCP image must load eagerly. Lazy-loading it adds a render delay and tanks LCP — a measured CWV regression in nearly every audit.
• "Image search traffic doesn't convert." It converts at 50-80% of web search rates depending on vertical, and is often the cheapest discovery surface for visual products. Worth optimizing.