Key Takeaways:

• Alt text describes your image in a simple, descriptive phrase
• Alt text is important to include as part of image SEO optimization so Google can surface your images in relevant searches
• Alt text should not be seen as one isolated event, but rather one piece of SEO as a whole.

What Is Alt Text? A Complete Guide to Image SEO Optimization

Alt text at its core describes images on your website. Each image on your site has two components. The first is what your visitors see. The second is what search engines and screen readers read. Alt text is the bridge between the two, and a lot of websites either ignore it completely or use it wrong.

In this guide we will cover what alt text actually is, why it’s important to SEO and how to write it in a way that works for both Google and real people.

What Is Alt Text?

Alt text (short for alternative text) is a written description attached to an image in HTML. When an image fails to load, that description appears in its place. When a screen reader encounters an image, it reads that description aloud to the user. And when a search engine crawls your page, it uses alt text to understand what the image actually contains.

Here is what that looks like in HTML:

<img src=”running-shoes.jpg” alt=”red trail running shoes on a dirt path”>

That alt attribute is also alt text. The difference between blank, generic, and well-written alt text has a measurable impact on how your pages rank and how accessible your site is.

Why Alt Text Matters for Image SEO Optimization

Alt text matters for image SEO optimization because it helps Google understand the images better. It does this by giving the pixels that Google’s crawlers process from visual content context, since Google doesn’t see images the way humans do. It tells Google what the subject is, what it shows, and how it relates to the content surrounding it.

From an image SEO optimization standpoint, alt text is one of the few direct signals you control. Google Images drives a good amount of search traffic, and pages with descriptive alt text are more likely to surface for relevant image searches. This compounds with your overall on-page SEO effort. If you have already done the work of building a holistic SEO strategy around keyword relevance, your images should reflect that same intent.

Accessibility Is Not Optional

Alt text was originally designed for accessibility, and that is still its most important function. Screen readers used by visually impaired users read alt text aloud to describe images. Without it, those users have no way to understand what an image is showing.

Google has been increasingly explicit about rewarding sites that treat accessibility seriously. Beyond rankings, it is a legal consideration for many businesses, particularly those covered by ADA guidelines.

Images Without Alt Text Are Invisible to Search Engines

Without Alt text, it’s hard for search engines to see that image actually exists. You could have stunning product photography or screenshots that reinforce your content, but if those images have no alt text, they are basically invisible to Google. This is the same principle that applies to crawling and indexing your entire site. Search engines can only work with what they can read and understand. Images with no alt text do not contribute to your topical relevance or keyword signals.

How to Write Alt Text for Images: The Core Principles

While writing alt text is not complicated, it does take intention and consistency at scale to be the most optimized and effective.

Be Specific and Descriptive

Alt text should describe what is in the image, not what you wish it said. If you have a photo of a chef plating food, the alt text should describe that scene, not just say “food photo” or leave it blank. Here are some examples of weak vs. strong alt text. 

Weak: image.jpg

Weak: photo of food

Strong: chef-plating-a roasted-salmon-dish-with-herbs-at-kitchen counter

Work Your Keywords In Naturally

Alt text is a good place to include target keywords, but only when they make sense in context. You shouldn’t force in a keyword just because you want that signal. If the image actually depicts what the keyword describes, include it. If it does not, leave it out.

For example, if you sell trail running shoes and the image shows someone wearing them on a mountain, writing “trail running shoes on a mountain trail” is both accurate and keyword-relevant. That is the sweet spot.

Keep It Concise

Most alt text should be under 125 characters. Screen readers often cut off longer descriptions, and Google does not need a long text to understand an image. Write one tight, descriptive sentence that captures the key information.

Skip Decorative Images

As important as alt text is, not every image needs alt text. Purely decorative images, like a generic background pattern or a divider line, should have an empty alt attribute (alt=””) rather than a filler description. This tells screen readers to skip the image entirely, which keeps the experience clean for visually impaired users.

Never Keyword Stuff

Just like how you shouldn’t keyword stuff in your content for SEO, you also shouldn’t keyword stuff when writing alt text. Writing alt=”red running shoes buy running shoes discount running shoes” will not get you anywhere. It is a very obvious sign to Google you’re trying to game the system and in the long run, will hurt you. Alt text stuffed with keywords creates a poor experience for screen readers and is explicitly called out in Google’s quality guidelines. One relevant keyword, used naturally, is all you need.

Alt Text Best Practices by Image Type

Different types of images require slightly different approaches to alt text. Here is how to handle the most common scenarios.

Product Images

Include the product name, key visual attributes (color, material, size if visible), and any context that would help a buyer. If it is a variation-specific image, that should be reflected in the alt text too.

Example: matte black 14-inch laptop sleeve with side zipper pocket

Infographics and Charts

These require more explanation than a simple photo. Summarize the key data point or takeaway the image communicates. If the infographic is complex, consider adding a text summary below it as well for both SEO and accessibility reasons.

Example: bar chart showing 40% increase in mobile search traffic from 2022 to 2024

Screenshots and UI Images

Describe the interface element being shown and what action is being demonstrated. This is especially important in technical content or tutorials where the screenshot is core to the instruction.

Example: Google Search Console performance report showing impressions and clicks over 90 days

Headshots and Team Photos

Include the person’s name and role if the image is meant to identify them. For decorative team culture photos, a brief description of the scene is enough.

Example: Sarah Kim, Head of Marketing at Visible Factors, speaking at a marketing conference

Alt Text and Technical SEO: What Else to Know

Alt text is the most visible part of image SEO, but it’s only part of a broader picture. Here are a few additional factors worth keeping in mind.

File Names Matter Too

Google reads your image file names before it reads alt text. A file named DSC_00324.jpg tells Google nothing. A file named red-trail-running-shoes.jpg gives it useful context before the alt attribute even comes into play. Rename your images with descriptive, hyphenated file names before uploading them.

Image File Size and Page Speed

Oversized images slow your site down, which directly affects both user experience and rankings. Alt text optimization means nothing if your images take four seconds to load. Compress images before uploading, use modern formats like WebP where supported, and use lazy loading for images below the fold. These are the same technical fundamentals that matter throughout your SEO crawling and indexing setup.

Structured Data for Images

If your site uses schema markup, image objects can be referenced within structured data for articles, products, and recipes. This gives Google additional context about how an image relates to the content on the page and can increase your chances of appearing in rich results and Google Images features.

Quick Alt Text Checklist

To make things simple, we included a quick checklist to run through before publishing any page with images:

• Every content image has a descriptive alt attribute
• Decorative images use alt=”” (empty, not blank)
• Alt text is under 125 characters per image
• Target keywords are used only where they naturally fit the image
• No keyword stuffing or generic fillers like “image” or “photo”
• Image file names are descriptive and hyphenated
• Images are compressed and appropriately sized for the web
• Structured data references key images where applicable

How Alt Text Fits Into a Broader Image SEO Optimization Strategy

Alt text is one piece of image SEO optimization, but it works best when it is part of a larger on-page SEO effort. Keyword-relevant alt text reinforces the topical focus of your page. Descriptive file names help Google understand your content before it even loads the image. Compressed, properly-sized images support site speed and Core Web Vitals performance. Together, these signals contribute to how Google evaluates your page overall.