Image SEO and Alt Text That Serves Users and Google
By CodexierPublished 5 min read
Alt text is often treated as an SEO chore: a place to repeat the keyword. That misses its purpose. Alt text is what a screen reader reads aloud to a person who cannot see the image, and what shows when the image fails to load. Written for that person, it also tells search engines what the image shows. This guide covers how to write good alt text, when an image should have none, and the technical details that decide whether your images appear in image search.
Alt text for people first
Good alt text answers one question: what would a person miss if they could not see this image? For a product photo, it is the product and its key visible feature. For a photo of your team at work, it is who and what. For a chart, it is the conclusion the chart supports. Keywords belong only where they naturally describe the image; stuffing them in makes the page worse for screen reader users and brings no benefit in search.
| Image | Weak alt text | Better alt text |
|---|---|---|
| Product photo | shoe | Black leather winter boot with a lined shaft and ridged rubber sole |
| Team photo | cleaning company Stockholm cleaning services | Two cleaners wiping down office desks in an open-plan office |
| Before-and-after | image1 | Bathroom before and after renovation, new tiles and walk-in shower |
| Chart | chart | Line chart showing enquiries rising after the new booking page launched |
When images need no alt text
Not every image carries information. Background textures, decorative dividers and icons next to a text label add nothing for a screen reader user, and describing them adds noise. These should have an empty alt attribute (alt with nothing inside the quotes), which tells assistive technology to skip them. Leaving the attribute out entirely is different and worse: some screen readers then read the filename aloud.
- Decorative images and background graphics: empty alt
- Icons with a text label next to them: empty alt
- Icons used as the only content of a button or link: alt describing the action, such as ”Search”
- Logos: the company name, and if it is a link to the start page, that the link goes there
- Images of text: the same text in the alt, or better, real text instead of an image
This is also a legal matter for many organisations: the accessibility requirements that apply to more Swedish websites since 2025 follow WCAG, where text alternatives are a basic criterion. Our guide to accessibility law for company websites explains who is covered.
Filenames and captions
Search engines read more than alt text. A filename like vinterkangor-svart-lader.jpg says more than IMG_4821.jpg. Visible captions are read by almost everyone who looks at an image and give search engines strong context. The text around the image matters as well: an image placed next to the paragraph it illustrates is easier to understand, for people and for Google, than one in a gallery with no text.
Filenames
Short, descriptive, lowercase, words separated by hyphens. Skip å, ä and ö in filenames to avoid encoding problems.
Captions
Use them where the image needs context: case photos, products in use, charts.
Surrounding text
Place images next to the text they illustrate, not in isolated galleries.
Formats and sizes
Images are usually the heaviest part of a page, and speed affects both users and search. Serve WebP or AVIF, scaled to the size they are displayed at, with several sizes offered so phones do not download desktop images. Set width and height so the layout does not jump while images load. Lazy-load images below the fold, but never the main image at the top of the page, which should load immediately. Our guide to image optimisation for speed goes into the technical detail.
Image search visibility
Image search matters more for some businesses than others. Webshops, restaurants, interior designers, builders and anyone whose work is visual can get real traffic from Google Images and from images shown in normal search results. To appear, images must be crawlable (not blocked by robots.txt or loaded only by scripts), included in the page's HTML or an image sitemap, and ideally connected to structured data, such as a product's image in Product markup. Our guide to structured data shows how.
When you do not need help: if your site has a few dozen images, you can go through them yourself in an afternoon with this guide. Our SEO audit and technical fix makes sense for large webshops and sites with thousands of images, missing alt text at scale or images that are not being indexed. To talk it through, book a short call.
Frequently asked questions
How long should alt text be?
Usually one short sentence. There is no strict limit, but screen reader users hear all of it, so say what matters and stop.
Should alt text include my keyword?
Only if it naturally describes the image. Keyword-stuffed alt text makes the page worse for screen reader users and does not help rankings.
Do all images need alt text?
All images need the alt attribute, but decorative ones should have it empty so assistive technology skips them.
Can AI write alt text for my images?
It can draft descriptions at scale, which is useful for large catalogues. Review them, because AI describes what it sees, not why the image is on the page.
Thousands of images and no alt text?
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