Image SEO: Alt Text, File Names and Fast-Loading Images

Images make websites engaging: product photos, project screenshots, team portraits and diagrams. But they are also the most common reason pages load slowly, and many are invisible to search engines and screen readers because they lack descriptions. Image SEO fixes both problems. Here is how to do it well.

What is alt text and why does it matter?

Alt text (alternative text) is a short written description of an image, added in the page code. Screen readers read it aloud for visually impaired visitors, browsers show it if the image fails to load, and search engines use it to understand what the image shows. Good alt text improves accessibility and helps images appear in image search.

How do you write good alt text?

• Describe what the image shows and why it matters on the page.
• Be concise: usually a short phrase or sentence.
• Be specific: "Stainless steel 6-burner commercial cooker with oven" beats "cooker".
• Include context where useful, such as a location or project name.
• Do not stuff keywords or start with "image of".
• Purely decorative images can have empty alt text, but meaningful images always need a description.

Alt text examples

Image	Weak alt	Better alt
Project screenshot	website	Homepage of the Masion real estate website showing property search
Team photo	team	Blessedave developers reviewing a website design in the Nairobi office
Product photo	sofa seo nairobi best sofa	Grey three-seater fabric sofa with solid wood legs
Diagram	chart	Diagram of the M-Pesa STK Push payment flow from checkout to confirmation

Why do file names matter?

A descriptive file name such as stainless-steel-gas-cooker-6-burner.webp gives search engines another clue, while IMG_4382.jpg gives none. Use lowercase words separated by hyphens and rename files before uploading.

Which image formats should you use?

Modern formats such as WebP and AVIF deliver similar visual quality at much smaller file sizes than older JPEG and PNG files. Use them for photos and screenshots, with JPEG fallbacks only if your platform needs them. Use SVG for logos and simple icons, because they stay sharp at any size.

How do you keep images fast?

1. Resize images to the largest size they are displayed, not the camera's original resolution.
2. Compress them; most photos look identical at much lower file sizes.
3. Serve responsive sizes so phones download smaller versions.
4. Lazy-load images below the fold so they load only when needed.
5. Prioritise the main image above the fold so it loads first.
6. Set width and height so the layout does not jump while images load.
7. Use a CDN to deliver images from servers close to visitors.

Does image placement matter?

Yes. Place images near related text, use captions where helpful and make sure the surrounding content explains the image's context. Search engines use the whole page, not just the alt text, to understand what an image shows.

What about structured data for images?

For articles, products and businesses, structured data can reference a main image, for example the product photo in product schema or the featured image in article schema. This helps search engines choose the right image for rich results and shopping listings.

How do you audit images on an existing site?

• Run PageSpeed Insights on key pages to find oversized images.
• Use a crawler to list images missing alt text.
• Check that product and project images have descriptive file names.
• Look for images loaded at desktop size on mobile.

At Blessedave we recently audited our own site so every meaningful image carries alt text, including project screenshots, author photos and article covers.

Who should write alt text?

The person who knows what the image shows: the product team for products, the project lead for project photos, the author for article images. Make alt text a required field in your content system so it is written when images are uploaded, not months later.

Example: speeding up a portfolio

An interior design studio's portfolio pages loaded full-size camera photos of several megabytes each. After converting images to WebP at display sizes, adding lazy loading, setting dimensions and writing alt text describing each space, the pages loaded far faster on mobile and the project images began appearing in image search for descriptive queries.

Get your images optimised

Our website design team builds automatic image optimisation into every site, and our SEO and AEO service audits images on existing sites. Read also why website speed matters and website accessibility.