Image SEO means setting up your website's photos so Google can find them, understand them, and show them fast. Google's own guidance says to use standard img tags and write short alt text. It also says to give files descriptive names. Serve images small and fast in a format such as WebP or AVIF.
How does Google find your images?
Google looks for images inside the src attribute of an img tag. This includes images placed inside a picture element, according to Google Search Central. Google does not index images used only as CSS backgrounds. Supported formats include BMP, GIF, JPEG, PNG, WebP, SVG, and AVIF, and the file extension should match the file's type. Pick a supported format, add it as an img tag, and skip CSS-only backgrounds for anything you want found in search.
What makes a strong alt text and file name?
Alt text is the attribute Google calls most important for image metadata. Google uses alt text along with computer vision and the surrounding page content to understand what a picture shows. It also helps people using screen readers. Good alt text stays plain and in context. Stuffing it with keywords creates a poor experience for readers. It can also get a website flagged as spam. Google's own example of good alt text reads "Dalmatian puppy playing fetch."
File names play a smaller part. Google calls them "very light clues," so a short, descriptive name such as my-new-black-kitten.jpg works better than a generic one like IMG00023.JPG. Google also reads captions, titles, and the text sitting near a photo. Place images close to the content they relate to. Keep them on the pages where that content lives.
Our guide to website accessibility covers the accessibility fixes to make first.
How should you serve images so pages load fast?
Images often make up the largest part of a page's size, according to Google. Checking that weight with PageSpeed Insights shows where it falls. For responsive images, use srcset or a picture element, always paired with a fallback src. Set width and height on every image, or reserve space with a CSS aspect-ratio, so the page doesn't shift as it loads.
Speed ties straight into Largest Contentful Paint, a measure explained by web.dev. It should reach 2.5 seconds or less at the 75th percentile of page loads. Images, video posters, and CSS background images can all count as the LCP element on a page. Google Search Central notes that good Core Web Vitals line up with what its core ranking systems already look to reward. Our guide to Core Web Vitals covers the full set of scores a business website should aim for.
One more speed rule: don't lazy-load anything that should show up right away. Google Search Central points out that lazy-loaded content still needs to load once it appears in the viewport. Google doesn't scroll or click through a page.
How does Google pick the thumbnail for your page?
According to Google's Search Central documentation updates, Google began using schema.org markup to choose a page's thumbnail in Search and Discover as of March 2026. It does this through primaryImageOfPage or the image field on the main entity, along with the og:image tag. Google's guidance asks website owners to pick an image that is relevant and high resolution. It also asks them to avoid logos, images with text, and extreme aspect ratios.
These same image SEO steps also cover generative AI search. Google Search Central's AI search guide notes that businesses already following image SEO best practices are already optimizing for it.
Do you need an image sitemap?
Not for every website. An image sitemap helps Google find images it might otherwise miss, such as ones loaded through JavaScript, according to Google Search Central. This can stand alone or get added to an existing sitemap, and it may list image URLs hosted on a CDN domain. Treat an image sitemap as a safety net for discovery, something to add if your images aren't showing up on their own.
Frequently asked questions
Does alt text help SEO?
Yes. Google calls alt text the most important attribute for image metadata and uses it, along with computer vision and page content, to understand what a picture shows. It also helps people who use screen readers navigate a page.
What image format is best for Google Search?
Google supports BMP, GIF, JPEG, PNG, WebP, SVG, and AVIF, with WebP and AVIF sitting alongside the older formats. Google lists these as supported formats.
Do image file names matter for SEO?
A little. Google treats file names as "very light clues," so a short, descriptive name helps more than a generic camera file name, though it won't carry an image on its own.
Do I need an image sitemap for my business website?
Only if some of your images might otherwise go unseen by Google, such as those loaded through JavaScript. An image sitemap helps with discovery and isn't required for every website.
Why does Google show the wrong thumbnail for my page?
Check your og:image tag and any schema.org image markup, since Google uses these to choose a page's thumbnail in Search and Discover. Point them at a relevant, high-resolution photo, and avoid logos and images with text.
Image SEO comes down to plain, descriptive images that load fast and point Google to the right thumbnail.
For help setting this up on your website, see TygerLabs' web design services.
