Image optimisation is no longer just a design or performance task. It directly affects how pages load, how content appears in Google Images and other visual search features, and how users experience your site. Google supports image indexing for common formats, including BMP, GIF, JPEG, PNG, WebP, SVG, and AVIF, and it uses surrounding page context, filenames, and alt text to understand what an image shows.
A well-optimised image can help a page rank better, improve click-through rates based on visual results, and reduce load time. A poorly optimised one can slow the page, weaken Largest Contentful Paint, and make the content harder for both users and search engines to interpret. web.dev notes that modern formats like WebP and AVIF usually compress better than JPEG or PNG, which can improve load speed and help LCP.
Why image optimisation matters
People rarely read a page word by word from the start. They scan. Images help them process information faster, break up long blocks of text, and decide whether the page is worth engaging with.
Search engines have adapted to that reality. Google’s image SEO guidance recommends using descriptive text near images, placing images in relevant context, and making sure image URLs are crawlable and indexable. It also says image optimisation can improve how your content appears on Google Images and other search surfaces.
That means image SEO now supports three goals at once: better user experience, better search visibility, and better technical performance.
Use the right image formats
The old advice to focus only on JPEG, PNG, and SVG is outdated. Google now supports WebP and AVIF in addition to the traditional formats. JPEG is still a solid choice for photographs, PNG is useful where transparency or precise graphics matter, SVG remains ideal for vector-based logos and icons, and WebP or AVIF are often better options for the web when browser support and workflow allow it.
In practice:
- use JPEG for standard photos when modern-format delivery is not available
- use PNG for graphics needing transparency
- use SVG for logos, icons, and simple vector illustrations
- use WebP or AVIF where possible for smaller file sizes and better performance
Balance quality, dimensions, and file weight
Image quality should always be high enough for the user, but not heavier than necessary. Large images are one of the biggest performance drains on the web, and web.dev explicitly warns that image assets often do the most damage to loading performance.
A modern workflow should:
- export images at the size they will actually be displayed
- serve responsive variants for different screen sizes
- compress files before uploading
- avoid uploading oversized originals and shrinking them only with CSS
For high-density screens, serving sharper variants is still important, but responsive image delivery is the better long-term solution than simply uploading everything at 2x size.
Keep images on your own domain or image CDN
If image files live on third-party hosts you do not control, attribution and traffic can become messy. A better setup is to serve them from your own domain, subdomain, or a properly configured image CDN. Chrome’s developer guidance recommends image CDNs because they can automate optimisation and modern format delivery.
Write descriptive filenames
Filenames still help search engines interpret images. Google recommends filenames and alt text that describe the image.
Instead of: IMG_5839.jpg
Use: gopro-12-black-front-view.jpg
Use lowercase letters, hyphens between words, and a description that matches the actual image.
Use alt text properly
Alt text is one of the most important image SEO signals because it helps search engines understand image content and improves accessibility for users with screen readers. Google explicitly recommends descriptive, useful alt text.
Good alt text should describe the image clearly and naturally.
Bad alt text: cake
Better alt text: chocolate cake with berries and dark glaze
Do not stuff alt text with repeated keywords. Write for clarity first.
Place images near relevant text
Google says it uses the text on the page to learn more about images. That means image placement matters. If an image appears next to highly relevant text, headings, and captions, search engines are more likely to understand the relationship correctly.
Put important images close to the section they support. Avoid placing critical meaning only inside the image itself, because search engines still rely heavily on surrounding HTML text to interpret visual assets.
Use structured data where relevant
If an image is part of a recipe, article, product, or another eligible search feature, structured data helps Google understand the page and image relationship more precisely. Google’s structured data documentation says image URLs used in structured data must be crawlable and relevant to the page. It also supports image metadata for Google Images, including creator and licensing details.
Include images in sitemaps when needed
Google can discover images through normal page crawling, but image sitemaps or image entries in XML sitemaps can help with discovery, especially on large sites or when images are loaded in ways that make crawling harder. Google Search Central still supports image SEO best practices through sitemap-based discovery.
Prioritise performance
A strong image SEO process should always include performance checks. PageSpeed Insights and Lighthouse commonly flag oversized images, missing responsive delivery, poor compression, and missed next-gen format opportunities. Chrome’s Lighthouse documentation recommends compressing images, serving responsive images, using lazy loading, and using modern formats like WebP.
Use original images when possible
Original images are not a direct ranking factor by themselves, but they can improve perceived quality, help your page stand out, and reduce the chance that your visuals look generic or duplicated. In competitive verticals, that matters more than people think.
Final thoughts
Image optimisation works best when handled as a system, not a one-time task. Choose the right format, keep files lightweight, use descriptive filenames and alt text, place images in relevant context, and make sure performance stays strong. Done properly, image SEO improves both rankings and usability.
