Image alt text SEO comes down to one job: describe what the image shows, in the context of the page, in a short plain sentence. Google says alt text is the most important attribute for giving it metadata about an image, and it uses that text alongside computer vision and the page content to understand the picture. The same text is read aloud by screen readers. So one good sentence serves both audiences. Nice deal.
The catch is that not every image needs a description. Some need an empty alt, some need the link destination instead, and a chart needs more than any alt attribute can hold. This guide walks through those branches, with examples you can copy.
How Does Image Alt Text SEO Work in Google?
Google’s image SEO best practices are unusually direct here. The page calls alt text “the most important attribute” for image metadata and says it also “improves accessibility for people who can’t see images on web pages, including users who use screen readers or have low-bandwidth connections.”
Two jobs. One field. For search, alt text helps Google match your image to queries in Google Images and understand what a page is about. For people, it replaces the image when they can’t see it. In my experience the second job is the better guide for writing, because text that works when read aloud almost always works for Google too.
One more job. People forget it. Google’s link best practices note that when an image is a link, its alt text acts like anchor text. A linked logo with no alt is a link with no words.
The Four Questions That Decide Your Alt Text
I don’t write alt text by feel anymore, because after years of auditing sites where the same logo had five different descriptions and half the product photos said “IMG_0042”, I wanted a repeatable order that any writer on a team could follow without asking me. I run each image through the order used in the W3C Web Accessibility Initiative’s alt decision tree, which asks roughly these questions:
- Does the image contain text? If that text is already on the page as real text, or it’s there for visual effect only, the alt can be empty. If the text appears nowhere else, the alt should include it.
- Is the image a link or a button? If removing it would make the link unclear, the alt describes where the link goes or what the button does.
- Does the image add meaning to the page? A simple photo gets a short description. A graph or diagram gets a short alt plus the full information somewhere on the page.
- Is it purely decorative? Then it gets an empty alt,
alt="".
Those four answers change the output completely. The same photo of a laptop might need “Dell XPS 13 in silver, open on a desk” on a product page and nothing at all as a background flourish on a blog header.
The Main Path: Informative Images
Most images on a normal site are informative, whether that’s a photo of the product, the team, the finished kitchen or a screenshot of a settings screen, and they’re the ones worth your writing time. For these, I write one sentence that answers “what would a reader miss if this image didn’t load?”
If the image shows something specific, name it specifically. “Dalmatian puppy playing fetch” is Google’s own “best” example, and it beats “puppy” because it carries the breed and the action.
If the surrounding paragraph already says what the image shows, keep the alt shorter and add only what the text doesn’t.
If you can’t decide what matters in the photo, go back to why it’s on the page. That reason is the alt text.
A few habits I’ve kept for years. Skip “image of” or “picture of”, since screen readers already announce it as an image. Put the most useful words first. And stop when the sentence is done; I rarely need more than 10 to 15 words, although there’s no official Google limit.
<!-- Illustrative example: informative image -->
<img src="walnut-standing-desk-oak-legs.jpg"
alt="Walnut standing desk raised to standing height with a monitor arm">
Branch 1: When the Image Is Decorative
Decorative images get alt="". Nothing else. That’s an empty value, not a missing attribute, and the difference matters. With the attribute missing, many screen readers fall back to reading the file name, so a user hears something like “hero underscore banner underscore final dot jpg”. With alt="", the screen reader skips the image quietly.
What counts as decorative? Background textures, divider flourishes, stock photos that add mood but no information, and icons sitting right next to text that already says the same thing. A magnifying glass icon beside the word “Search” is decorative in that spot.
Honestly, this is where SEO advice and accessibility advice collide most. I still see plugins and “SEO checklists” that push a keyword into every single image, decorative ones included. That makes a page worse for screen reader users and adds nothing Google needs. If the image carries no meaning, let it be silent.
Branch 2: Linked Images, Buttons and Logos
When an image is the only content inside a link or button, the alt text describes the action or destination, not the picture. A magnifying glass button gets “Search”, not “magnifying glass”. A printer icon that prints the page gets “Print this page”.
Logos? Same logic. In the header, your logo usually links to the homepage, so I write the company name plus the destination, like “Skyranko home”. A logo in a “clients” or “partners” strip that doesn’t link anywhere just needs the company name. And a logo placed next to the company name in text can take an empty alt, because the name is already there.
How Should You Handle Charts, Screenshots and Infographics?
A chart can’t be summed up in 12 words. Don’t try. The W3C calls these complex images and splits the job in two: a short alt that says what the image is, and the full information in text nearby, such as a data table or a paragraph under the chart.
So a bar chart might get alt text like “Bar chart of monthly organic clicks, January to June”, with the actual numbers in a table below it. Screenshots of software work the same way. The alt says which screen it is, and the steps in your text explain what to click. Infographics are the worst offenders in my audits, because the whole point of the image is text that exists nowhere else on the page, so neither Google nor a screen reader can read it.
Alt Text for Product Images
Product images are where alt text earns real money, since shoppers use Google Images to compare products. I write product alt text with the attributes a buyer would use to tell variants apart: brand, product name, colour, material, and the angle or detail shown.
When a product has six gallery images, each one should say what’s different about that shot. “Red leather tote bag, front view” and “Red leather tote bag, interior zip pocket” are both useful. Six copies of the product name aren’t. My guide to product page SEO covers the rest of the page around those images.
Good vs Bad Alt Text Examples
These are illustrative examples I wrote for this post, not taken from any client site.
| Image | Bad alt text | Better alt text | Why |
|---|---|---|---|
| Product photo of running shoes | “shoes” | “Nike Pegasus 41 in blue, side view” | Brand, model, colour and angle help shoppers and Google |
| Staff photo on a bakery About page | “bakery best bakery cakes bakery near me” | “Four bakers in aprons standing outside the shop front” | Describes the scene instead of stuffing keywords |
| Decorative wave divider | “seo wave divider image” | alt="" | Carries no meaning, so screen readers should skip it |
| Search button icon | “magnifying glass” | “Search” | A functional image describes the action |
| Line chart of traffic | “chart” | “Line chart of weekly visits, March to May” plus a data table | Complex image needs the data in text |
| Header logo linking home | missing alt | “Company name home” | Acts as anchor text for the link |
| Image with a quote in it | “quote” | The full quote text | Text in the image exists nowhere else |
Where Does Keyword Stuffing Start?
Google’s wording is blunt: avoid filling alt attributes with keywords, because it “results in a negative user experience and may cause your site to be seen as spam.” Its own bad example is a puppy photo with a string of dog breeds and “cheap dogfood” crammed into one alt.
My rule? Simple. If the keyword naturally describes what’s in the image, use it. If you have to bend the sentence to fit it in, cut it. A photo of a plumber fixing a sink can say “plumber replacing a kitchen sink trap”; it can’t honestly say “best emergency plumber Austin cheap plumbing services”.
Alt Text vs Title vs File Name vs Caption
These four fields get mixed up constantly, and I’ve seen teams spend a week rewriting title attributes nobody reads while the alt fields on their best-selling product pages sat completely empty, so it’s worth knowing what each one does.
| Field | Who sees it | What it’s for | My advice |
|---|---|---|---|
| Alt text | Screen readers, Google, anyone whose image fails to load | Replaces the image with text | Always set it, or set it empty for decorative images |
| Title attribute | Mouse users as a hover tooltip | Extra advisory info | Optional, and not a replacement for alt |
| File name | Google, and people who download the image | Short hint about the subject | Google suggests short descriptive names like my-new-black-kitten.jpg |
| Caption | Every visitor | Visible context under the image | Use it when the image needs explaining to everyone |
Google says it extracts information about an image’s subject from the page content, “including captions and image titles.” So captions do help. I just don’t repeat the caption word for word in the alt, because screen reader users would hear it twice.
Can You Trust AI-Generated Alt Text?
AI captioning is now built into plenty of CMS plugins and office tools, and I get why teams like it. It fills thousands of empty fields in an afternoon. My take is that it’s a decent first draft and a poor final answer.
The problem? Context. A model can see “a woman holding a phone” but it doesn’t know the page is about a refund process and the phone shows the refund screen. It also can’t tell when an image is decorative, so it describes dividers and background shapes that should be silent. And it sometimes guesses wrong about brands, people and text in the image. I’d use AI output only as a starting point, then have a person review every image on your top pages.
How to Audit Alt Text Across a Whole Site
On a site with a few hundred pages, I start with a crawler. Screaming Frog’s SEO Spider has an Images tab with filters for “Missing Alt Attribute”, “Missing Alt Text” and “Alt Text Over 100 Characters”, and there are similar reports in most site audit tools. Chrome’s Lighthouse accessibility audit also flags images without an alt attribute, one page at a time.
Now the trap. “Missing Alt Text” in Screaming Frog means the attribute exists but is empty, and on a well-built site many of those are correct decorative images. So I export the list, sort by page importance, and review by hand. Fix the missing attributes everywhere, then write real alt text for the images on pages that earn traffic or sales first.
If you want a baseline on a WordPress site, the alt text lives in the Media Library per image, but blocks can override it per post. Check both. And if images are CSS backgrounds, remember that Google says it doesn’t index CSS images, so an important photo needs a real img element. Broader image optimization for SEO, like file size, formats and lazy-loading, is a separate job and I won’t cover it here, apart from one habit: set width and height on every image, which my guide on how to fix CLS explains.
Image Alt Text Decision Matrix
| If the image… | And… | Then |
|---|---|---|
| Shows something the reader needs | The text around it doesn’t say it | Short, specific description |
| Shows something the reader needs | The text already describes it | Short alt adding only what’s missing |
| Is a link or button | It’s the only content in the link | Describe the action or destination |
| Is a chart, diagram or infographic | It holds data or text | Short alt plus the full data in page text |
| Contains text | That text appears nowhere else | Put the text in the alt |
| Adds only visual style | Nothing is lost if it’s hidden | alt="" |
| Is a product photo | There are several gallery shots | Name the product plus what each shot shows |
When Should You Get Help With Alt Text?
A small site can fix alt text in an afternoon. A store with 20,000 product images, a JavaScript gallery that strips alt attributes, or a legal accessibility complaint is a different job. For accessibility compliance, bring in an accessibility specialist who audits against WCAG, since alt text is only one of many requirements.
For the SEO side, image work is part of the on-page audit we run in our SEO service. If you’re a photographer, my SEO for photographers guide covers portfolio images in more depth. And if you’d like a second pair of eyes first, request a free SEO audit.
Frequently Asked Questions
Does Alt Text Help SEO Rankings?
Alt text helps Google understand an image, which matters most for ranking in Google Images and for image links. Google calls it the most important attribute for image metadata. It won’t rescue a weak page on its own, but missing or stuffed alt text is an easy fix I include in every on-page audit.
How Long Should Alt Text Be?
Google doesn’t publish a character limit. I aim for one sentence, usually under 15 words, and move anything longer into a caption or the page text. Screaming Frog flags alt text over 100 characters as a review prompt, which is a sensible checkpoint rather than a rule from Google.
Should Every Image Have Alt Text?
Every img element should have an alt attribute, but not every image needs words in it. Decorative images should use an empty value, alt="", so screen readers skip them. Informative, linked and text-containing images all need real alt text that matches their purpose on the page.
Is the Image Title Attribute Important for SEO?
The title attribute shows as a tooltip on hover and is optional. It doesn’t replace alt text, and screen readers handle it inconsistently. I spend my time on alt text, file names and captions first, and only add a title when it gives the reader something extra.
Last updated: September 2026 by Mizanur Rahman
