Alt Text SEO: The Overlooked Signal That Costs You Traffic

Alt text SEO is the practice of writing descriptive alternative text for images so that search engines can index them accurately and serve them in relevant results. Done well, it extends your keyword footprint, improves image search visibility, and strengthens page relevance without requiring a single new piece of content.

Most sites treat alt text as an accessibility checkbox. That framing is not wrong, but it is incomplete. Alt text is also a signal, and ignoring it means leaving a relatively low-effort ranking lever unused while your competitors quietly collect image search traffic you never even knew existed.

Why Alt Text Matters More Than Most SEOs Admit

I have sat in enough SEO audits to know that alt text almost always appears in the “quick wins” column. The implication is that it is easy and therefore minor. I would push back on that framing. Quick to fix does not mean low impact. The two things are not the same, and conflating them is how sites end up with years of unoptimised image libraries sitting on otherwise well-maintained domains.

Google cannot see images the way a human can. It reads the surrounding text, the file name, the page context, and the alt attribute to understand what an image depicts. That alt attribute is your direct line of communication with the crawler. When it is missing, vague, or stuffed with keywords, you are either saying nothing useful or actively creating confusion.

The SEO value operates on two levels. First, it reinforces the topical relevance of the page. If you are writing about commercial kitchen equipment and your images have precise, descriptive alt text, every image is contributing to the crawler’s understanding of the page. Second, it opens a separate traffic channel through Google Images. For categories like fashion, food, interiors, real estate, and product-led e-commerce, image search is not a rounding error. It is a meaningful source of first-touch visits.

Alt text is part of a broader set of on-page signals that shape how Google reads and ranks a page. If you want to understand how all of those signals fit together, the Complete SEO Strategy hub covers the full picture, from technical foundations through to content and link signals.

How Google Uses Alt Text as a Ranking Signal

Google has been explicit that alt text helps it understand image content. What is less discussed is how that understanding feeds into broader page-level relevance scoring. When a crawler processes a page, it is building a model of what the page is about. Every text element contributes to that model: the title, the headings, the body copy, the anchor text of internal links, and yes, the alt attributes of images.

This means that a page with ten images and no alt text is, from the crawler’s perspective, a page with ten gaps in its content map. The page is telling Google less than it could. In competitive verticals, that kind of omission compounds. Your competitors who are writing precise alt text are incrementally building a denser, more coherent relevance signal on pages that are otherwise comparable to yours.

The image search channel operates slightly differently. Google Images has its own ranking logic, and alt text is one of the primary inputs. File names matter too, as does the surrounding text and the authority of the host page. But alt text is the most direct signal, and it is the one you have the most control over. A well-optimised image on a well-optimised page can rank in image search for queries that your main content is not targeting, which effectively expands your keyword footprint without adding a word of body copy.

One thing worth understanding: Google’s image ranking is not purely about the image itself. The authority and relevance of the surrounding page matters significantly. An image with perfect alt text on a thin, low-authority page will not outrank a similar image on a well-established domain. Alt text is a signal, not a shortcut.

What Good Alt Text Actually Looks Like

The standard advice is to “be descriptive.” That is correct but incomplete. The more useful framing is to be descriptive in a way that serves both the crawler and the user. Those two things are not in conflict, but they do require a bit of discipline to get right simultaneously.

Good alt text does three things. It describes what is in the image accurately. It connects that description to the topic of the page. And it does so in natural language, not a keyword list. “Black leather office chair with adjustable armrests” is good alt text for a product image on a furniture e-commerce page. “Chair office chair best office chair buy office chair” is not. The second version tells the crawler nothing coherent and tells a screen reader user even less.

Length matters too. Alt text does not need to be a sentence. It rarely needs to exceed 125 characters. Beyond that, you are writing for the sake of writing, not for the crawler or the user. The discipline of brevity actually helps here, because it forces you to identify the one or two most important things about an image rather than trying to capture everything.

Context matters as much as description. The same image can warrant different alt text depending on the page it appears on. A photograph of a chef plating a dish on a restaurant homepage might be described as “head chef plating a seasonal tasting menu dish.” The same photograph on a catering services page might be described as “corporate catering presentation by [restaurant name].” The image is identical. The alt text should reflect the page context, not just the image content.

When I ran agency teams managing large e-commerce clients, this context-sensitivity was where most of the value was being lost. The same product images were appearing across category pages, product pages, and blog content with identical alt text copied from the product database. That is not wrong exactly, but it is a missed opportunity. Tailoring alt text to page context is the difference between treating images as a content asset and treating them as a database field.

Decorative Images, Functional Images, and When to Leave Alt Text Empty

Not every image needs alt text. This is a point that gets glossed over in most SEO guides, and it matters for both accessibility and crawl efficiency.

Decorative images, those that exist purely for visual aesthetics and add no informational value, should carry an empty alt attribute: alt=””. This tells screen readers to skip the image entirely, which is the correct behaviour. It also tells the crawler that the image is not content-bearing, which is accurate. Filling decorative images with keyword-rich alt text is a form of manipulation that adds noise to your relevance signal rather than strengthening it.

Functional images are a different category. These are images that serve a purpose: buttons, icons, logos, infographics, charts, and product photographs. These should always have alt text, and the alt text should describe the function or content of the image, not its aesthetic qualities. A logo alt text should include the brand name. A chart alt text should summarise what the chart shows. A button image should describe the action it triggers.

Infographics deserve particular attention. They are frequently shared, frequently linked to, and frequently indexed in image search. They also tend to contain a lot of information that the alt text cannot fully capture. The practical approach is to write alt text that describes the infographic’s main point and to ensure the surrounding page content covers the detail. That combination serves both the crawler and the user without requiring you to compress an entire infographic into 125 characters.

Common Alt Text Mistakes That Undermine SEO

The most common mistake is missing alt text entirely. This is usually a process problem rather than a knowledge problem. Images get uploaded without alt text because the workflow does not require it, and no one goes back to fix the backlog. On a site with thousands of images, that backlog can represent a significant amount of untapped relevance signal.

The second most common mistake is using file names as alt text. “IMG_4892.jpg” or “photo1.jpg” as alt text is worse than empty. It is actively misleading. File names should be descriptive too, but they are a separate signal from alt text and should not be used as a substitute.

Keyword stuffing is the third mistake, and it is more damaging than most people realise. I have seen audits where every image on a page had identical alt text loaded with the page’s target keyword. That pattern is not invisible to Google. It reads as manipulation, and it creates a poor experience for users relying on screen readers. One relevant, descriptive phrase per image is the correct approach. Repetition across images on the same page is a flag, not a strategy.

Over-description is a subtler problem. Writing a paragraph of alt text for a simple product image is not helpful. It dilutes the signal and creates a poor accessibility experience. The goal is precision, not comprehensiveness.

Finally, there is the problem of generic alt text. “Image of product” or “photo of team” tells the crawler almost nothing. It is technically present but functionally useless. The effort required to write a specific, descriptive alt text versus a generic one is minimal. The difference in signal quality is not.

If you want to understand how individual on-page decisions like these interact with your broader ranking performance, Moz’s analysis of failed SEO tests is a useful reminder that not every optimisation works in isolation and that context shapes outcomes more than any single tactic.

Alt Text at Scale: How to Fix a Large Image Library

One of the more uncomfortable conversations I have had with clients is explaining that their 50,000-image product catalogue has no alt text and that fixing it is not a weekend project. The instinct is to automate the whole thing, which is understandable but usually produces mediocre results at scale.

The practical approach is to prioritise by traffic and commercial value. Start with the pages that drive the most organic sessions and the product categories with the highest revenue contribution. Fix those first. Then build a process so that every new image uploaded from that point forward gets proper alt text before it goes live. The backlog does not disappear overnight, but you stop making it worse while you work through it systematically.

AI-generated alt text has improved considerably and can be a reasonable starting point for large catalogues. The important word there is “starting point.” Auto-generated descriptions tend to be accurate about what is in an image but blind to page context and keyword relevance. They need human review and editing, particularly for high-value pages. Using them to generate a first draft and then editing for context is a defensible workflow. Using them as a complete solution is not.

For sites using a CMS with structured content, the most efficient approach is to build alt text into the content entry workflow rather than treating it as an afterthought. If editors are uploading images and the CMS does not prompt for alt text, they will not write it. The process has to make the right behaviour the default behaviour.

Crawl tools can help you identify missing alt text at scale. Most SEO platforms will flag images without alt attributes in a standard audit. The output gives you a prioritised list to work through. What it cannot do is write the alt text for you, and that is where the real work sits.

Alt Text and Image Search as an Acquisition Channel

Image search gets underestimated as an acquisition channel because it sits outside the standard keyword tracking workflow. Most teams are measuring organic traffic by landing page and by text-based query. Image search traffic often lands on the same pages but via a different entry point, and unless you are looking at Google Search Console’s Search Type filter, you may not be tracking it separately.

The industries where image search has genuine commercial value are fairly consistent: fashion, interiors and home decor, food and recipe content, real estate, travel, automotive, and product-led e-commerce more broadly. If your business sits in one of these categories and you are not optimising for image search, you are not competing for a meaningful slice of available traffic.

For real estate in particular, visual search intent is high. Buyers and renters search for properties by looking at images as much as by reading listings. Ahrefs covers the SEO considerations for real estate in some depth, and image optimisation sits within a broader set of signals that matter in that vertical.

The traffic from image search tends to have different behaviour characteristics than text search traffic. Bounce rates can be higher because users are browsing visually rather than arriving with a specific transactional intent. But for brand awareness and top-of-funnel reach, image search delivers real impressions on real queries, and those impressions compound over time as your image library grows and gets indexed.

The measurement piece matters here. I have seen teams dismiss image search as marginal without ever actually measuring it. If you are not segmenting your Search Console data by search type, you do not know what image search is contributing. That is not a data problem. It is an attention problem. The data is there. Someone has to look at it.

How Alt Text Fits Into a Broader On-Page SEO Strategy

Alt text does not operate in isolation. It is one input into a page-level relevance model that Google is building from dozens of signals simultaneously. Understanding where alt text sits in that hierarchy helps you allocate effort appropriately.

Title tags, headings, and body copy carry more weight than alt text in most cases. If those elements are weak, fixing your alt text will not rescue the page. Conversely, if your core on-page signals are strong, well-optimised alt text adds an incremental layer of relevance that can make a difference in competitive situations where pages are otherwise closely matched.

The compounding effect is worth taking seriously. A page with strong title, headings, body copy, internal links, and alt text is a more coherent signal than a page that is strong on some of those dimensions and weak on others. SEO is not about finding the one lever that moves rankings. It is about building a consistent, well-maintained set of signals across a site. Alt text is one of those signals, and neglecting it is a small drag on every page it appears on.

I spent several years managing large-scale SEO programmes across retail and financial services clients. The pattern I saw repeatedly was that teams would invest heavily in link building and content creation while leaving basic on-page hygiene, including alt text, in a state of chronic neglect. The link investment was delivering diminishing returns while the on-page gaps were quietly suppressing the pages those links were pointing to. Fixing the on-page issues often produced more measurable movement than the next round of outreach.

It is also worth noting that alt text has a direct relationship with page accessibility. Google has stated that it uses accessibility signals as part of its quality assessment. A page that is genuinely accessible to users with visual impairments is also a page that is providing clearer signals to the crawler. The two goals are aligned, not competing.

For teams running structured SEO testing, Semrush’s work on split testing on-page elements is a useful reference for understanding how to measure the impact of individual changes rather than assuming they work. The same discipline applies to alt text: if you are making changes at scale, build in a way to measure the before and after, even if the measurement is imperfect.

Alt text is one piece of a larger on-page picture. The Complete SEO Strategy hub covers how all of these elements connect, from technical configuration through to content depth and authority building, so you can see where alt text fits relative to everything else competing for your optimisation budget.

A Practical Workflow for Writing Alt Text That Works

The goal is to make good alt text the default output of your content process, not an audit item that gets addressed every eighteen months. That requires a clear, repeatable workflow rather than a set of guidelines that editors read once and forget.

Start with the question: what is this image communicating to a user who cannot see it? If the answer is “nothing in particular, it is just decoration,” use an empty alt attribute. If the image is communicating something, describe that something in plain language, connect it to the page topic, and keep it under 125 characters.

For product images, include the product name, the key distinguishing feature, and if relevant, the brand. “Stainless steel 1.7L cordless kettle with keep-warm function” is more useful than “kettle” and more useful than “best kettle buy now kettle stainless steel kitchen.”

For editorial images, describe what is happening in the image and why it is relevant to the article. A photograph of a marketing team in a meeting room on an article about agency culture might be described as “marketing agency team in a strategy session.” That tells the crawler and the user something specific and relevant.

For charts and data visualisations, summarise the key finding rather than describing the visual format. “Bar chart showing 40% year-on-year growth in mobile search queries” is more useful than “bar chart with blue bars.” The finding is the content. The format is incidental.

Build a review step into your publishing process. Before any page goes live, alt text should be checked alongside title tags and meta descriptions. It takes thirty seconds per image. The cumulative value across a site compounds significantly over time, and the cost of doing it properly is genuinely low relative to the return.

About the Author

Keith Lacy is a marketing strategist and former agency CEO with 20+ years of experience across agency leadership, performance marketing, and commercial strategy. He writes The Marketing Juice to cut through the noise and share what works.

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