Images do more work than most people realise. They carry meaning for the people who cannot see them, they feed Google context about your page, and they are often the single biggest reason a page loads slowly. Get them right and you help three audiences at once: screen reader users, search engines, and everyone waiting for your page to appear.

This is a quick, practical guide to image SEO and alt text. No fluff, just the things we actually check when we audit a site.

What alt text is for

Alt text is the written description of an image. It has two main jobs.

First, accessibility. If someone uses a screen reader, the alt text is read aloud in place of the image. If an image fails to load, the alt text shows instead. This is the primary reason it exists, and it is a legal and ethical point, not just an SEO one.

Second, context. Google cannot see an image the way you can. Alt text, along with the file name and surrounding text, tells search engines what the image shows. That matters for your normal page ranking and for Google Images, which still sends real traffic for product, recipe, and how-to content.

How to write good alt text

Describe what is in the image, plainly, as if you were telling someone on the phone what they are missing.

Good: "Oak dining table with six chairs in a bright kitchen."

Bad: "image1234", "product photo", or an empty alt attribute.

A few rules we stick to:

• Keep it concise. Around one short sentence is plenty. You do not need "image of" or "photo of" at the start; screen readers already announce it as an image.
• Be specific. "Red leather handbag with gold clasp" beats "handbag".
• Include the keyword only if it fits naturally. Stuffing alt text with keywords reads badly to a screen reader and looks like spam to Google. Describe the image honestly and the right words usually appear on their own.
• Match the context. The same photo might need different alt text on different pages depending on why it is there.

When to leave alt text empty

This surprises people: sometimes the correct alt text is nothing at all.

If an image is purely decorative, a background flourish, a divider, an icon that sits next to a text label that already says the same thing, then it should have an empty alt attribute (alt=""). That tells a screen reader to skip it rather than read out noise. An empty alt attribute is deliberate and correct. A missing alt attribute is not the same thing, and it is a common mistake.

File names matter too

Before you upload, rename the file. Cameras and phones produce names like DSC_0049.jpg, which tell Google nothing.

Use short, descriptive, hyphenated names: oak-dining-table-kitchen.jpg. Lowercase, words separated by hyphens, no spaces or underscores. It is a small signal, but it is free and it reinforces what the alt text and page say.

Compression: the part people skip

Here is where image SEO meets site speed. A single uncompressed photo straight off a phone can be four or five megabytes. Put a few of those on a page and you have a slow, heavy page that frustrates visitors and drags your Core Web Vitals down.

What we do on every build:

• Resize to the dimensions actually used. There is no reason to serve a 4000 pixel wide image into a 600 pixel slot.
• Compress. Most photos can lose a large chunk of file size with no visible quality loss.
• Use modern formats. WebP and AVIF are far smaller than old JPEG and PNG files at the same quality. Most browsers support them now.
• Use responsive images so phones download a smaller file than desktops.

If you want the full picture on why this matters commercially, we go deeper in the real cost of a slow website.

Lazy loading and layout shift

Two more technical points that sit under image SEO.

Lazy loading means off-screen images only download when the visitor scrolls near them. That speeds up the initial load. Add loading="lazy" to images below the fold, but not to your main hero image, which you want to load immediately.

Layout shift is when an image loads late and shoves the rest of the page down, making people lose their place or tap the wrong thing. Always set width and height attributes (or a CSS aspect ratio) so the browser reserves the space before the image arrives. Google measures this as part of Cumulative Layout Shift, and it affects ranking.

A quick checklist

Before you publish a page, run through this:

• Every meaningful image has descriptive alt text.
• Decorative images have an empty alt attribute.
• File names are descriptive and hyphenated.
• Images are resized to the dimensions used.
• Images are compressed and served as WebP or AVIF where possible.
• Width and height are set to prevent layout shift.
• Below-the-fold images are lazy loaded; the hero is not.

Where alt text fits in the bigger picture

Alt text alone will not rank a weak page. It is one honest signal among many, and it sits inside the wider on-page work of good titles, headings, structured content, and internal links. Treat it as part of the craft of building a page properly, not a box to tick after the fact.

The nice thing about image SEO is that doing it well helps real people first. A fast page with clear descriptions serves someone on a slow connection, someone using a screen reader, and Google all at once. That alignment is rare in SEO, so take it when you can get it.

If you want this handled properly across a whole site, from compression and formats to responsive delivery, it is part of how we build and maintain pages on our engineering work.