Are alt attributes really essential for your SEO, or just a nice-to-have for accessibility?

Why does Google place such a strong emphasis on alt attributes?

Google can't "see" an image like a human does. The engine relies on surrounding text (caption, adjacent paragraphs, page title) and especially on the alt attribute to understand what the image is about. Without an alt, the crawler can only guess at best, relying on the file name (often uninformative) or completely ignoring the image.

From an accessibility standpoint, screen readers read the alt attribute aloud for visually impaired users. A missing or poorly written alt makes the content incomprehensible for this audience. Google has taken accessibility seriously for several years — it's a quality signal for the site, even if the direct impact on ranking remains unclear.

Does the alt attribute influence ranking in traditional search (text)?

Directly, no. The alt attribute does not improve your page's position in text SERPs in isolation. However, it enriches the overall semantic context of the page: if you publish an article about the Paris marathon with a photo of runners and an alt of "runners crossing the finish line of the Paris marathon," Google better understands the article's topic.

Indirectly, this can influence thematic understanding and thus ranking on long-tail queries. But the main impact lies in Google Images, where the alt is a major ranking factor. If your business depends on Image traffic (e-commerce, galleries, portfolios), neglecting the alt cuts you off from a significant source of visits.

What happens if I put an empty or generic alt?

An empty alt (alt="") is acceptable — and even recommended — for decorative images with no informational value (separators, backgrounds, purely aesthetic icons). This avoids polluting the screen reader user's experience with noise.

On the other hand, a generic alt like "image," "photo," "illustration" adds no value. Google ignores these hollow alts, and you waste an opportunity to contextualize. If you automate alt generation (misconfigured CMS), check that default values are not empty strings or raw file names ("IMG_1234.jpg").

• Every informative image must have a descriptive and contextualized alt.
• Decorative images can have an empty alt (alt="") to avoid disrupting screen readers.
• The alt enriches the semantic context of the page and boosts ranking in Google Images.
• A generic alt or a file name serves no purpose for Google or for accessibility.
• Aim for 5 to 15 descriptive, factual words without keyword stuffing.

Is this recommendation consistent with what we observe in practice?

Yes, absolutely. Field tests show that images with descriptive alts rank better in Google Images than those without alts or with generic alts. It is also observed that pages with well-written alts tend to rank better on long-tail queries where the image provides context (e.g., "microservices architecture diagram" rather than just "architecture").

However, the direct impact on text ranking remains difficult to isolate. We know that Google uses visual context to refine thematic understanding, but it is impossible to quantify how many positions you gain by adding alts. What is certain: the absence of an alt causes you to lose Image traffic, and that is measurable.

What nuances should be added to this statement?

Mueller discusses accessibility and SEO as if they are two separate benefits. In reality, accessibility has become an indirect quality signal for Google. Websites conforming to WCAG (Web Content Accessibility Guidelines) tend to perform better overall, even if Google does not explicitly admit it.

Another nuance: not all alts are created equal. An alt stuffed with keywords ("best running shoe Nike cheap promotion") is counterproductive. Google detects spam, and screen readers read unbearable gibberish. The alt must be written for a human first, with relevant keywords appearing naturally. [To verify]: Does Google use image analysis (Vision API) to compare the alt with the actual content of the image? No official confirmation, but tests suggest that alts completely disconnected from the image may be ignored.

In what cases does this rule not fully apply?

Images in lazy loading or JavaScript may cause issues. If the crawler does not see the image at the time of initial rendering, the alt is not taken into account. Ensure that your lazy-loaded images remain accessible to the crawler (native loading="lazy" attribute, not a homemade script that completely hides the image).

Another edge case: identical image galleries with nearly identical alts. If you have 50 photos of a product from different angles with the same alt, Google may consider this internal duplicate content. Vary the alts to describe what changes ("frontal view," "detail of the sole," "close-up of the zipper").

What should you do concretely to optimize alt attributes?

Audit your existing images. Use Screaming Frog, Sitebulb, or a home-built crawler to list all tags and identify those without alts, with empty alts on important images, or with generic alts. Prioritize strategic pages (product sheets, landing pages, key articles) and correct them first.

For each image, ask yourself: "If I couldn't see this image, what should I know to understand its role in the content?" Describe factually what is visible, integrating the context of the page. Example: for a photo of a smartphone, "iPhone 15 Pro front view showing the OLED screen and titanium design" is better than "smartphone" or "iPhone 15 Pro iPhone 15 Pro buy cheap".

What mistakes should be avoided when writing alt attributes?

Do not duplicate the title or caption in the alt. If the image already has a