Image Alt Text Optimization Best Practices for Better SEO

Image alt text optimization best practices that actually move the needle

A client sent me a screenshot last month that still makes me laugh. Their accessibility audit flagged 412 images with the alt text "image" or "IMG_4471.jpg". Four hundred and twelve. On a site with maybe 60 unique products. They'd spent a year optimizing meta descriptions and never touched a single alt attribute.

Here's the thing: image alt text optimization is one of those tasks everyone agrees matters and almost nobody does properly. It sits at a weird intersection — part accessibility requirement, part SEO signal, part plain common sense. And unlike most SEO work, getting it right takes minutes, not months.

I've rewritten alt text across e-commerce catalogs, editorial sites, and one very stubborn nonprofit whose board kept confusing alt text with image captions. This is what I've learned.

What are the best practices for writing alt text on images?

Write alt text as if you're describing the image over the phone to someone who can't see it and needs to know only what matters in that context. That's the whole job. Everything else is detail.

In practice, the rules I follow look like this:

• Describe the function, not the appearance — a magnifying glass icon next to search is "Search", not "magnifying glass icon"
• Skip "image of" and "picture of". Screen readers already announce that it's an image
• Match the tone of the surrounding page. A terse product page and a warm editorial piece shouldn't share the same phrasing
• If the image does something (links to a page, triggers a tooltip), the alt text does that thing too
• Punctuation matters. End with a period if the alt text is a full sentence, skip it if it's a fragment

That last point sounds fussy. It isn't. Screen readers pause differently depending on punctuation, and a missing period in a long description turns into one breathless run-on announcement. Small thing, real impact.

The three-category rule

Every image you place falls into one of three buckets, and each requires a different approach:

Decorative — the image adds visual texture but no information. Backgrounds, section dividers, purely aesthetic flourishes. These get alt="". Empty. Not missing, not "decorative image". Empty tells screen readers to skip it entirely.

Functional — the image is a button, a link, or an interactive control. The alt text describes what it does: "Add to cart", "Open navigation menu", "Play video".

Informative — the image carries meaning the surrounding text doesn't. Photographs in articles, screenshots in tutorials, charts in reports. These need a real description, and the length depends on how much meaning the image holds.

I'll admit, I spent my first year writing alt text only for the informative category and leaving decorative images with nothing at all. That's a mistake, and it took a screen reader user's complaint to show me why. Missing alt makes software guess — it might read the filename, it might announce nothing at all. Empty alt is a deliberate instruction. Silence on purpose.

What is the ideal length for image alt text?

Roughly 100 to 125 characters. That's the practical ceiling most screen readers handle before they either truncate or become exhausting to listen to.

It's not a hard technical limit — nothing breaks if you go to 150. But the 125-character mark lines up with what the average reader can hold in mind from a single announcement before the sentence fragments. Push past it and you're asking someone to remember an entire paragraph they heard once, in passing.

Image type	Recommended length	Example
Decorative	0 characters	alt=""
Icon or button	1–4 words	"Search", "Download PDF"
Product photo	40–80 characters	"Leather hiking boot, brown, side profile"
Editorial photograph	80–125 characters	"Rowers practicing on a foggy river at dawn, viewed from the eastern bank"
Complex chart	Short alt + long description nearby	"Bar chart: 2025 sales by region" with full data in the body text

When longer is actually right

Scientific figures break the character limit on purpose. A graph showing experimental results can't be summarized in 125 characters without losing the finding. In that case, write a short alt text that says what the figure is, and put the full explanation in the body text. The alt text functions as a signpost; the prose does the analytical work.

The pattern I use: alt text tells you the figure exists and what it depicts, then the paragraph directly below explains it in full. Screen reader users reach the alt text, know what's coming, and get the details from the prose.

Does alt text help with SEO for images?

Yes, but not in the way most people assume. Alt text is not a hidden keyword field. Google's image search uses it as one signal among many — alongside the filename, surrounding text, page title, and structured data.

Where it actually pays off: image search traffic and accessibility compliance. If you run an e-commerce site, image search sends real buyers. Someone searching "black ceramic planter with drainage tray" is a more qualified visitor than someone searching "plant pots". Images that rank for those long-tail terms convert better because the query matches the exact product.

What I've watched fail, repeatedly: stuffing the same keyword into twenty image alt texts on one page. Google's spam systems flag that the same way they flag keyword-stuffed anchor text. Worse, screen reader users hear the same six words twenty times in a row and give up.

Keywords without spam

Here's the rule that actually works: if a sighted user heard the alt text read aloud and wouldn't notice anything odd, it's fine. If it sounds like a robot reciting search terms, rewrite it.

• Good: "Hand-thrown stoneware mug in matte blue, holding 350 ml"
• Bad: "handmade mug stoneware mug blue mug ceramic mug artisan mug pottery mug"

The first would be a normal thing to hear. The second is a keyword dump. Nobody needs a rule beyond that.

What are the best practices for alt text in 2026?

The fundamentals haven't shifted, but three things have gotten sharper this year because of how browsers and assistive tech now behave.

First, AI-generated alt text is now embedded in most CMS platforms. WordPress, Shopify, and Squarespace all offer automatic alt generation. It's better than it was two years ago, and still not good enough to ship without review. I tested it on 50 product images from a client's catalog last month. Useful on maybe 30 of them. The other 20 were technically accurate and useless — describing backgrounds, missing the actual product detail buyers cared about.

Second, alt text is being ingested by AI agents and voice interfaces. When someone asks a voice assistant what's on a page, the assistant reads whatever's there. Alt text now shapes how AI systems describe your content back to users. Sloppy alt text becomes a sloppy spoken summary.

Third, contrast and motion descriptions are creeping into accessibility guidelines. Alt text can now legitimately mention things like "dark mode version" or "animated, autoplay, 3 seconds" when those details affect how the image communicates. It's a small shift, but it matters for compliance.

Alt text vs image description

These get confused constantly. Alt text is what assistive technology announces in place of the image. An image description is a longer, structured explanation that lives elsewhere on the page — often in a disclosure widget or a linked page. Complex infographics need both. Alt text says "Bar chart comparing 2019 and 2024 emissions by country", the description does the analysis.

Alt text for logos

A logo that links to the homepage gets alt text like "Company name — home". A logo sitting in a footer next to the company name in text should probably be alt="" to avoid duplication. The rule is the same as everywhere: what does the image do here, in this specific place?

The practice that matters most

None of this means anything if you write alt text once and never look at it again. Content changes. Products get updated. Images get swapped without anyone touching the alt text that described the old version.

What works: audit your alt text every six months, and treat it like copy, not metadata. Sit with a screen reader turned on for twenty minutes a week. You'll hear problems no guideline will teach you.

The part nobody mentions in these guides is that alt text forces you to be clear about what your images are actually doing. Half the images on most sites are decorative noise nobody asked for. If you can't write alt text for an image without strained phrasing, that's not a copywriting problem. It's a signal the image might not need to be there at all.