The alt attribute of an image is a text description embedded in the HTML markup that explains what is depicted in the image. It was originally created to improve accessibility so that users with visual impairments could obtain information using screen readers. Later, alt became an important element of SEO, especially in the context of visual optimization and expanding entry points through Google Images. Its use allows search engines to “understand” an image, since crawlers do not interpret pixels directly, but read text signals.
Unlike titles and captions, alt text is not visible on the page to the average user if the image loads correctly. But if for some reason it does not display — for example, due to a slow connection, resource blocking, or errors along the way — alt text becomes what the visitor sees. Its main purpose is to provide search engines with a textual interpretation of the image. It is through alt that Google determines how relevant an image is to the content of the page, which queries to show it for, and whether to consider it as part of the relevant search results at all.
If you run a professional SEO studio, alt should not be a “default” element added by the CMS. It is a conscious structural element: just as important as the title, h1, and meta descriptions. Alt text can not only improve your site’s rankings, but also expand your audience reach, including users who come through Google Images or use adaptive technologies.
Why alt is more than just SEO
Although image SEO is one of the reasons why alt is considered mandatory, its role is not limited to search traffic. From an accessibility (Web Accessibility) perspective, it is a basic element. People with visual impairments who use screen readers rely on alt as their only source of understanding what is in an image.
According to international WCAG standards, its absence on important images is considered a violation. Therefore, alt is also about ethics, inclusivity, and correct content presentation. From a technical standpoint, alt is read first in the HTML structure of an image and can be used in a snippet displayed in visual search results.
In addition, it serves as a backup text option if the image cannot be loaded: in this case, the browser displays the alt text instead of an empty space. In conditions of low internet speed or limited devices (e.g., old phones), this preserves the context of the page.
Read also: What is rel=next and rel=prev.
In modern Google algorithms, alt is also used to form extended snippets, understand the topic of a page, generate previews in image carousels, and even in Google Lens. This makes alternative text not just an auxiliary channel, but a key channel of communication between an image and a search.
How to write alt descriptions correctly and where people go wrong
For alt to work effectively, it must be concise, accurate, and essentially describe the content of the image. There is no need to write “photo,” “image,” or “picture” — this is already clear from the context. Alt should reveal what is depicted, why it is important, and how it relates to the main topic of the page.
Examples:
- Bad: alt=”Photo”
- Bad: alt=”Buy a house cheap furniture Kiev SEO”
- Good: alt=”Wooden desk with drawers in an office interior”
- Good: alt=”Screenshot of the Search Console panel with an indexing error”
One sign of a good description is if you can close your eyes and imagine what is depicted based on the alt text. It is also important that the text does not duplicate the title, contain keyword stuffing, or be formulaic.
The most common mistakes:
- leaving empty alt attributes on key images
- using alt for keyword stuffing (stuffing up to 5 keywords)
- duplicating the same alt throughout the site
- confusing alt with title — although the latter is not mandatory and is often ignored by bots
- using auto-generated alt at the CMS level, without clarifying the meaning
As part of an affordable SEO analysis of your website, a competent alt audit is a must. This is especially true if your website contains a lot of visual content: product catalogs, galleries, portfolios, infographics, presentations, work samples, or case studies.
Where alt is required and where it is not necessary
Alt is not necessary for all images. There are interface elements that are best left with an empty alt (alt=“”) — for example, backgrounds, decorative lines, and icons that do not carry any meaning. But everything related to the content of the page must be described. This applies to:
- product photos
- screenshots and diagrams
- employee portraits
- article covers
- logos
- banners with text
- infographics
- charts containing data
- images with text quotes
These are the images that Google indexes as part of the semantic core of the page. They participate in visual search results, influence behavioral metrics, and help reinforce the topic. It’s easy to understand whether alt is needed: if the image is important for understanding the material and the meaning is lost without it, then alt is needed.
Read also: What is a visual snippet.
How alt interacts with other attributes
In the context of image SEO, alt is just one element of visual optimization. Its effectiveness is enhanced if:
- the file name is descriptive and logical (e.g., seo-checklist-2024.jpg, not IMG_0582.jpg)
- the title attribute provides an extended explanation, although this is not mandatory
- the image is located next to the thematic text
- the correct heading structure is used around the image
- there is a caption if it is important for explanation
- the image loads quickly, is not blocked by robots.txt, and does not have a redirect
It is also important to note that alt works in conjunction with attributes such as loading=lazy, srcset, sizes, and other modern parameters. For example, loading=lazy delays the loading of the image, but alt can still be read by the bot in advance. This affects the accessibility rating and depth of perception of the page. Therefore, technical configuration is just as important as the description itself.
