Image SEO
What is image SEO?
Image SEO is the practice of optimising images so search engines can find, understand and rank them, and so they don’t slow the page down. It covers descriptive filenames and alt text, placing images near relevant text, modern formats and compression, correct sizing, lazy loading below the fold and image sitemaps or structured data where useful.
Google finds images through the src attribute of <img> elements; images set only as CSS backgrounds aren’t indexed as images. Google Images supports formats including JPEG, PNG, GIF, WebP, SVG and AVIF. Images are often the largest file on a page and frequently the Largest Contentful Paint element, so they matter for speed too.
Why image SEO matters
Image results bring traffic for visual searches such as products, recipes, design and places, and images can appear in the main SERP, in Discover and in product listings.
Unoptimised images are a common cause of slow pages and layout shift, which hurt user experience and Core Web Vitals.
How to optimise images for SEO
- Use original, relevant images rather than generic stock where you can.
- Give files descriptive names, such as sourdough-starter-day-5.webp.
- Write useful alt text and place images near related text or captions.
- Compress images and serve modern formats like WebP or AVIF, at the size they are displayed, with srcset for different screens.
- Set width and height attributes to prevent layout shift.
- Lazy-load images below the fold, but never the main image at the top of the page.
- Add images to structured data for products, recipes and articles where relevant.
Image SEO example
<img src="/img/oak-table-800.webp"
srcset="/img/oak-table-400.webp 400w, /img/oak-table-800.webp 800w, /img/oak-table-1600.webp 1600w"
sizes="(max-width: 600px) 100vw, 800px"
alt="Solid oak dining table set for six"
width="800" height="533" loading="lazy">Image SEO FAQ
What is the best image format for SEO?
WebP and AVIF usually give the smallest files at good quality and are supported by Google and modern browsers. Use SVG for logos and icons.
Do image filenames matter for SEO?
A little. Google says filenames can give it clues about an image’s subject, so descriptive names are better than IMG_4821.jpg.
Related SEO terms
Alt text is a short written description of an image in its HTML alt attribute. It helps screen reader users and tells search engines what the image shows.
An image pack is a row or block of image results inside Google’s main search results, linking to Google Images and the source pages.
Lazy loading delays loading images, iframes or other content until they are about to scroll into view, which speeds up the first load of a page.
Largest Contentful Paint (LCP)
Largest Contentful Paint (LCP) is a Core Web Vital that measures when the largest image or text block in the viewport appears. Good is 2.5 seconds or less.
Page speed is how quickly a page loads, shows its content and responds to input. Google measures it mainly through Core Web Vitals.
Cumulative Layout Shift (CLS) is a Core Web Vital that measures how much content moves unexpectedly while a page is used. Good is 0.1 or less.