Image SEO gets your images found in Google Images and keeps your pages fast, so buyers reach your products through a second route and stay long enough to enquire. The work covers descriptive alt text, short file names, a supported format, compression and a sitemap entry where Google misses an image. Alt text carries the most weight: Google calls it the most important attribute for image metadata and 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 you traffic from Google Images and keep your pages fast, and both effects feed your enquiries and sales. Images appear in image search results and alongside web results, so a well-described image gives buyers a second route to your page. Sharp images attract clicks, and large files slow the page. Google states that images are often the largest contributor to overall page size and recommends checking speed with PageSpeed Insights.
Which Ten Image SEO Practices Matter?
The ten practices cover what each image is, how you describe it and how it loads.
| # | Practice | What you do | Primary effect | Where it applies |
|---|---|---|---|---|
| 1 | Use original images | Show your own product, team, premises and data | Differentiation, brand recognition | Every page with a photo |
| 2 | Choose the right format | Match the format to the image type | File size, quality | Every image |
| 3 | Compress every file | Export at display size, then compress | Load speed | Every image |
| 4 | Name files descriptively | Replace camera defaults with plain words | Context for search engines | Every image |
| 5 | Write unique alt text | Describe the specific image in a sentence | Image search, accessibility | Every meaningful image |
| 6 | Serve responsive sizes | Use srcset or picture with a src fallback | Load speed on mobile | Large and hero images |
| 7 | Add images to a sitemap | List images Google misses | Discovery | Script-loaded or CDN-hosted images |
| 8 | Add structured data | Mark up the image property | Rich results eligibility | Product, recipe and video pages |
| 9 | Lazy load below the fold | Delay off-screen images | Initial load speed | Long pages and galleries |
| 10 | Test speed after changes | Compare before and after | Verification | Each batch of changes |
Ten image SEO practices. Source: Google Search Central, October 2026
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 Google advises matching the file extension to 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, so every page loads faster for your buyers. 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 reads the file name as a light clue to the subject, 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 one 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 Google lists the image property as 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 moves neither 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, and together they decide how many buyers find and stay on your pages. 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.