Optimizing Alt Tags for Images: Importance for Accessibility and SEO

Introduction to optimizing Alt tags

Alt tags are an often overlooked aspect of web search engine optimization (SEO). However, they play a crucial role both for your site’s accessibility and for its optimization for search engines (SEO). An Alt tag, or alternative text, is a brief description of an image, which is displayed when the image cannot be loaded on a web page. It is also used by assistive technologies, such as screen readers, to help visually impaired users understand the content of an image.

The importance of Alt tags for accessibility

In terms of accessibility, Alt tags are essential. They allow people who use screen readers and other assistive technologies to understand the content of your website. Without Alt tags, these users could miss important information and have a poorer user experience. Moreover, even those who do not use assistive technologies can benefit from Alt tags. For example, if an image does not load properly, the Alt tag can provide useful context.

The role of Alt tags in SEO

In addition to their vital role in accessibility, Alt tags also play an important role in search engine optimization. Search engines, like Google, cannot «see» images in the same way humans do, and therefore rely on Alt tags to understand their content. Well-optimized Alt text can help your site rank higher for relevant keywords and appear in image search results. Thus, Alt tags not only improve your site’s accessibility, but they can also lead to increased organic search traffic.

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Legacy of accessibility standards and role of the attribute alt

When Tim Berners-Lee published the first proposal for the World Wide Web in 1989, he implicitly introduced the notion of a universal internet where content would be readable by any machine. Very early on, the W3C understood that part of the population cannot absorb visual information and included in the HTML 2.0 specification (1995) the attribute alt. ., From there, regulatory bodies such as the American Section 508, the European Web Accessibility Directive and then the General Framework for Improving Accessibility (RGAA) in France, took up the idea and turned it into a legal obligation. Ignoring or poorly filling in an alt Alt tag therefore exposes you to fines or litigation, just like a store without an access ramp.

Netflix’s experience in 2016 illustrates the importance of these standards. After a class action lawsuit brought by the National Association of the Deaf, the platform had to overhaul its multimedia ecosystem to include captions and text descriptions. Even though Netflix mostly deals with video, the case boosted the entire sector: the number of companies carrying out WCAG compliance audits doubled the following year, and with it the attention paid to the attributes alt. .. In other words, the legislator has made «accessible” SEO an industry standard.

Direct impact on the user experience: from text-to-speech to offline browsing

On a well-designed site, the journey of a blind user differs little from that of a sighted user: they simply listen to the descriptions. A screen reader like JAWS translates the HTML structure into audio signals; the synthetic voice jumps from heading to heading, reads links and, when it reaches an image, automatically switches to the attribute alt. .. If it is empty or irrelevant («image1.jpg ), the experience becomes a labyrinth. User tests carried out by the University of Lyon show that 72 % of non-sighted participants leave a page if they encounter more than two images without a textual alternative.

But the issue is not limited to disability. When 3G connections struggle, sometimes the browser does not display the image and shows the text instead alt. In the archives of the New York Times website, viewing in airplane mode brings up descriptions such as «Front-page photograph of the Apollo 11 launch, July 16 1969 . The user understands the historical context despite the absence of visuals. Same scenario in countries where data costs are high; a simple Alt tag alt becomes the main channel of visual information.

Correlation between visual description and semantic relevance

Since the Hummingbird algorithm (2013) and especially RankBrain (2015), Google has enriched a page’s relevance using semantic signals. The attribute alt then plays a role equivalent to internal link anchors: it provides lexical context. If your product page mentions «waterproof Gore-Tex ® hiking shoes” and the image displays a alt generic like «shoes«, the algorithm loses an essential clue and the long-tail query “women’s goretex trekking boots” may slip away from you.

Conversely, Patagonia experimented in 2020 with rewriting 18,000 tags alt with key expressions taken from their internal search tool. Result: +12 % organic traffic on Google Images and +5.8 % e-commerce conversions. More interesting still: CTR on classic universal search increased by 2 points, proof that a clear description of images also strengthens the overall semantic coherence of the HTML document.

Technical SEO: how the tags alt influence indexing and ranking

Googlebot behaves like a browser without a graphical interface. It reads the markup, follows links, evaluates the structure, and records the text. Images, on the other hand, are handled by a separate processor that tries to recognize shapes through computer vision. To reduce this costly step, Google uses tags alt as a shortcut. A Searchmetrics study (2022) reveals that 30 % of the thumbnails displayed in the «Related images” section of a SERP come from pages where the main keyword appears in the attribute alt.

The influence doesn’t stop at the «Images« vertical. On the main SERP, the “Top Stories” block and rich results (recipes, products, how-to) include thumbnails. These thumbnails are weighted by the semantic relevance of the alt combined with the