Alt text is added where a website outputs a thumbnail—not to the directory or image file itself. Edit the image’s media record, content field, or HTML, then check how the thumbnail is used on the page. The right text depends on its purpose: describe meaningful content, explain an image link’s destination, or use an empty alt value for decoration.
What a directory does—and does not—control
A directory stores image files. Its name, the image filename, and a generated thumbnail size do not provide a considered text alternative to visitors using assistive technology. The alt attribute belongs to the image element rendered by the website.
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Find the system that outputs the thumbnail: a CMS media record or content field, a theme or template, or HTML written directly into a page. Add or review the alternative text there, and inspect the rendered page rather than assuming a particular file path or size controls it.
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Informative image
Describe the content or information a non-visual visitor needs from the image. Keep the wording concise and relevant to that page; the goal is to preserve the page’s meaning when the image is not available.
#1 Best Overall
Thumbnail that links somewhere
When the image is the only content in a link, its alternative text should communicate the link’s purpose or destination. Describe what following the link does, rather than merely listing visual details that do not help identify the link.
Decorative image
If the thumbnail adds no information and serves no function in its context, use an empty alt value: alt="". This lets assistive technology skip it. Do not omit the attribute as a substitute for deciding whether the image is informative or decorative.
Rank #2
Filename as alt text
A filename is not a reliable alternative. It may be unclear, include technical details, or fail to explain what the image does in context. WordPress accessibility guidance warns that if alt is omitted, a filename may be used or announced. Add an alt attribute and write text appropriate to the image’s role.
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WordPress: edit the media record and check the block
- In the WordPress dashboard, open Media → Library and select the image, or open its Edit Media screen.
- Enter the appropriate text in Alternate text and save the media record.
- If the thumbnail is in an Image Block, inspect the block’s own alt-text setting. A block can use wording suited to its particular placement when the image’s role differs from its general media use.
- View the published page and check the rendered thumbnail, including whether it is linked and whether the alternative communicates its purpose.
WordPress creates smaller image subsizes for display, and its wp_get_attachment_image() function can emit a thumbnail-sized image. A smaller generated file is still an image element: verify the output and its alt attribute, rather than relying on the filename or directory.
Drupal: separate file storage, image style, and alternative text
- Identify the image field used by the content type or media workflow. Drupal’s image module lets site builders configure the field, including a default directory for uploaded files.
- When attaching an image to content, enter its alternate text in the image field.
- Configure image styles for display transformations such as scaling or cropping. Those affect the displayed image, not what its alternative text should say.
- Check the rendered content to ensure the text fits the image’s purpose in that placement.
A storage directory determines where files go; an image style determines how an image is displayed; the alt value gives a text alternative. Treat these as separate settings.
Auditing existing Drupal records
The Drupal Image Alt Fallback project documents a filterable media table and configurable handling of empty alt values for Drupal 10 or 11 sites. It describes a transitional safety net, not a replacement for meaningful text stored on the media or file record. Check the project’s current compatibility, configuration, and fit before relying on it.
Rank #4
Direct HTML and templates
Give every relevant <img> an alt attribute. For example:
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<!-- Informative thumbnail -->
<img src="/images/blue-bicycle-thumb.jpg" alt="Blue bicycle leaning against a brick wall">
<!-- Image-only link: describe the link's purpose -->
<a href="/bikes/blue-city-bike/">
<img src="/images/blue-city-bike-thumb.jpg" alt="View the blue city bike">
</a>
<!-- Decorative thumbnail -->
<img src="/images/section-divider-thumb.jpg" alt="">These are illustrative examples: choose wording that accurately matches the actual image and page. In a template, check every place the image is rendered because the same asset can be informative in one context and decorative or link-bearing in another.
Verify the result on the page
- Inspect the page where the thumbnail appears, not just the directory or CMS file details.
- Confirm the rendered image has an
altattribute and that its text fits the image’s purpose in that context. - For an image-only link, check that its alternative makes the link’s purpose understandable.
- For a purely decorative image, confirm the value is exactly empty:
alt="". - When a reusable image appears in multiple placements, review each use; a single media-level description may not fit every context.
Common problems and fixes
The thumbnail still announces a filename
The rendered image may have no alt attribute, or a template may be outputting a different image than the CMS record you edited. Inspect the page output, then correct the relevant media record, block setting, field, or template.
The CMS alt text does not suit one placement
Image meaning depends on context. Review the local block or content field, or adjust the template output, so an image used as a link communicates that link’s purpose.
The thumbnail is cropped or resized
Resizing and cropping are display transformations. They do not supply alternative text. Keep the text focused on the meaning or function of the displayed image.
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Fallback behavior can provide a safety net, but generic or automatically supplied text may not communicate the image’s purpose. Store meaningful, context-appropriate text on the source media or file record wherever possible.
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