Images make pages easier to understand and more enjoyable to read, but they are also one of the most common reasons websites load slowly. Optimised properly, images help in three ways: they speed up your pages, they help Google understand your content and they can bring extra visitors from Google Images.
This guide covers image SEO best practice for 2026, based on Google's own documentation and what we see working on client sites.
Name images descriptively, write genuinely helpful alt text, use modern formats such as WebP or AVIF, compress files, serve the right size for each screen, lazy load images below the fold and place images near the text they support.
- Use short, descriptive file names and helpful alt text, written for people rather than stuffed with keywords.
- Google supports BMP, GIF, JPEG, PNG, WebP, SVG and AVIF; WebP and AVIF give the best balance of quality and size.
- Compress images, serve sensible dimensions with srcset and always keep a normal src fallback.
- Lazy load images further down the page, but never your main hero image.
In this article
Why image optimisation matters
- Page speed: large images are a common cause of slow pages, which frustrates visitors and can hold back rankings.
- Understanding: Google uses file names, alt text, captions and surrounding text to work out what an image shows.
- Extra traffic: well described images can appear in Google Images and visual search results.
- Accessibility: alt text describes images to people using screen readers.
1. Use descriptive file names
Google says file names give it very light clues about an image, and recommends names that are short but descriptive. Its own example is that my-new-black-kitten.jpg is better than IMG00023.JPG.
- Good:
kitchen-extension-leeds.webp - Poor:
IMG_4471.webporkitchen-extension-leeds-best-builders-cheap-kitchens.webp
2. Write helpful alt text
Alt text describes the image for people who cannot see it, and helps Google understand it. Google advises writing useful, information rich alt text that uses keywords appropriately and in context, and warns against stuffing alt attributes with keywords.
| Approach | Example |
|---|---|
| Missing | alt="" |
| Keyword stuffed | alt="builder Leeds builders Leeds kitchen builder Leeds" |
| Helpful | alt="Finished kitchen extension with bifold doors in a Leeds terrace" |
Purely decorative images can keep an empty alt attribute so screen readers skip them.
3. Choose the right format
Google supports images in BMP, GIF, JPEG, PNG, WebP, SVG and AVIF formats, and recommends that the file extension matches the file type.
- WebP: the best all rounder for photos and graphics, much smaller than JPEG or PNG at similar quality.
- AVIF: often smaller again, now widely supported by modern browsers.
- SVG: ideal for logos and icons, as it stays sharp at any size.
- JPEG and PNG: still fine as fallbacks, but rarely the best choice for new images.
4. Compress without losing quality
Most photos can be compressed significantly before anyone notices a difference. As a rule of thumb, aim for most content images to be well under 200KB, and resize photos to the largest size they will actually be displayed before uploading. A 4000 pixel wide photo shown at 800 pixels wastes bandwidth on every visit.
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5. Serve responsive images
Use the srcset attribute or the picture element to offer different sizes for different screens, so phones download smaller files than large desktop monitors. Google notes that some crawlers do not understand these attributes, so always include a standard src attribute as a fallback.
Set width and height attributes on images too. This lets the browser reserve the right space and stops the page jumping as images load.
6. Lazy load the right images
Lazy loading delays images until a visitor scrolls near them, which speeds up the first view of the page. Use it for images further down the page, but do not lazy load your main hero image. That image is often the largest element on the screen, and delaying it makes the page feel slower.
7. Put images in context
Google extracts information about an image from the page around it, including captions and nearby text. Place images close to the content they support, add captions where they help the reader and avoid putting important text inside images, where it is harder for search engines to read.
8. Help Google find your images
Use standard img elements rather than CSS backgrounds for important images, as Google does not index CSS background images. If you have many images that are hard to discover, an image sitemap can help.
Whether your customers search from Northampton, Liverpool or Leicester, Google rewards the same things: a useful site, a strong local presence and steady proof that people trust you. You can find every city we cover on our SEO locations page.
Image SEO checklist
| Check | Done well |
|---|---|
| File name | Short, descriptive, hyphen separated |
| Alt text | Describes the image clearly, no stuffing |
| Format | WebP or AVIF for photos, SVG for logos |
| Size | Resized to display size and compressed |
| Responsive | srcset with a src fallback, width and height set |
| Loading | Lazy load below the fold, not the hero |
| Context | Near relevant text, with captions where useful |
Image optimisation is one part of technical SEO. If your site feels slow or your rankings have stalled, our guide to why rankings drop covers other common causes.
Frequently asked questions
What is the best image format for SEO?
WebP is the best all round choice for most websites, and AVIF can be even smaller. Google supports BMP, GIF, JPEG, PNG, WebP, SVG and AVIF, so choose the format that gives the best quality at the smallest size.
Does alt text help SEO?
Yes. Google uses alt text, along with file names and surrounding content, to understand images. Write alt text that describes the image helpfully and avoid stuffing it with keywords.
What size should website images be?
Resize images to the largest size they will be displayed and compress them. Most content images can be well under 200KB without a visible loss in quality.
Should I lazy load all images?
Lazy load images further down the page, but not your main hero image or anything visible when the page first loads, as that can make the page feel slower.
