Image SEO makes each image findable in Google Images and cheap to load, through descriptive alt text, short file names, a supported format, compression and a sitemap entry where discovery fails. Alt text carries the most weight. Google calls it the most important attribute for providing image metadata, and it warns against stuffing it with keywords (Google Search Central, image SEO best practices). This guide gives ten practices in the order that returns the most value first.
Why Does Image Optimisation Matter?
Optimised images win traffic from Google Images and keep pages fast, and both effects feed conversions. Images appear in image search results and alongside web results, so a well-described image gives a second route to your page. Sharp images attract clicks, and large files slow the page. Google recommends balancing quality against file size and checking performance with PageSpeed Insights.
Which Ten Image SEO Practices Matter?
The ten practices cover what the image is, how it is described and how it loads.
| # | Practice | Primary effect |
|---|---|---|
| 1 | Use original images | Differentiation, brand recognition |
| 2 | Choose the right format | File size, quality |
| 3 | Compress every file | Load speed |
| 4 | Name files descriptively | Context for search engines |
| 5 | Write unique alt text | Image search, accessibility |
| 6 | Serve responsive sizes | Load speed on mobile |
| 7 | Add images to a sitemap | Discovery |
| 8 | Add structured data | Rich results eligibility |
| 9 | Lazy load below the fold | Initial load speed |
| 10 | Test speed after changes | Verification |
1. Use original images
Original photos and graphics separate your pages from sites that reuse the same stock files. Show your own product, team, premises and data. Original visuals also carry a consistent identity, and they give other sites an asset to credit with a link.
2. Choose the right format
Google Search supports BMP, GIF, JPEG, PNG, WebP, SVG and AVIF, and the file extension needs to match the real file type (Google Search Central). Use JPEG or WebP for photographs, PNG for graphics that need transparency, SVG for logos and icons, and AVIF where your tooling supports it and the saving justifies the effort.
3. Compress every file
Compress each image before upload. Export at the largest size the layout displays, then apply compression until quality loss becomes visible and step back one level. Automate the step in your build or media library so no editor skips it.
4. Name files descriptively
Use short, plain file names that describe the image, such as a product name or subject, with hyphens between words. Google treats file names as a light clue, so a clear name helps without carrying the ranking load. Replace camera defaults such as IMG_2041.
5. Write unique alt text
Write alt text that describes what the image shows, in a natural sentence, for people who are unable to see it. Screen readers read it aloud, and search engines use it to understand the image. Describe the specific image, leave decorative images with empty alt text, and never repeat one keyword string across a page.
6. Serve responsive sizes
Use the picture element or the srcset attribute so each device downloads a suitable size, and keep a fallback in the src attribute, as Google recommends. A phone then avoids the weight of a desktop hero image.
7. Add images to a sitemap
An image sitemap lists images Google otherwise misses, including images served from a CDN on another domain. Add it when scripts load images or when galleries hide them from the crawler. Standard pages with plain image elements need no extra file.
8. Add structured data
Image structured data makes an image eligible for badges and rich results in Google Images, and the image property is required for that eligibility. Add the markup that matches your content type, such as product, recipe or video, and keep every value identical to the visible page.
9. Lazy load below the fold
Lazy loading delays images until the visitor scrolls near them, which shortens the first load. Never lazy load the main hero image, because that delays the largest element a visitor sees. Confirm in the rendered page that lazy-loaded images still appear in the HTML Google processes.
10. Test speed after changes
Run PageSpeed Insights before and after each batch of image changes, and compare the largest contentful paint and total page weight. Record the result. A fix that does not move either number needs another look at the cause.
How Do Images Relate to Your Wider On-Page Work?
Images are one pass in a full on-page review, alongside titles, headings, content and speed. Add the image checks to your crawl export so alt-text and file-size gaps show up in the same report as the rest. Follow the complete sequence in the on-page SEO audit guide, and pair descriptive alt text on linked images with the rules in the anchor text guide.
For the wider programme, read what SEO is and see the technical SEO service.