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Image Alt Text for SEO and Accessibility: A Decision Guide
Good alt text communicates the image’s purpose in context. It is not a caption, a keyword field, or a requirement to describe every pixel.
Run a fresh DomainLens audit and use the report as your priority list.
Decide what would be lost if the image disappeared
Context changes the answer. A headshot next to a person’s name may need only that name; the same photograph in an article about protective equipment may need to describe the visible equipment.
| Image purpose | Alt approach | Example |
|---|---|---|
| Informative | Describe the information relevant here | “Mobile LCP improved from 4.2s to 2.1s after the release” |
| Functional/link | Describe the action or destination | “Download the Q2 accessibility report” |
| Decorative | Use empty alt | alt="" |
| Text rendered as image | Include the same essential words | “Acme — inventory for independent retailers” |
| Complex chart/diagram | Short identification plus nearby full explanation | “Checkout flow with three validation branches” |
| Product image | Identify distinguishing product traits | “Blue trail shoe, side view” |
Write the equivalent, not an inventory of pixels
- Begin with the useful information; “image of” is usually redundant.
- Use natural wording and only include a search term when it genuinely identifies the subject.
- Do not repeat the adjacent caption or paragraph verbatim when it already supplies the equivalent.
- Keep filenames, camera details, and decorative styling out unless they matter to the task.
- For a linked image, make the accessible name explain where the link goes rather than how the icon looks.
<!-- Decorative flourish: ignored by assistive technology -->
<img src="wave.svg" alt="">
<!-- Informative screenshot: purpose is clear -->
<img
src="canonical-conflict.png"
alt="Search Console showing a different Google-selected canonical">Common failures and their real fix
| Failure | Why it fails | Fix |
|---|---|---|
| Missing alt on informative image | Meaning is unavailable to non-visual users | Write the contextual equivalent |
| alt="image" or filename | Adds no useful information | Describe purpose/subject |
| Keyword list | Unreadable and not equivalent | Use one natural description |
| Decorative image with verbose alt | Creates noise | Use alt="" |
| CSS background carries content | No native text alternative | Use an img or provide equivalent visible text |
| Same alt on product gallery | Views cannot be distinguished | Describe relevant view/detail or mark redundant ones decorative |
Audit alt text with context, not a completeness percentage
Alt text is only one image SEO signal. Confirm that important images can be fetched, are not delayed beyond the user action that reveals them, and describe the same entity as the page markup. The image SEO guide covers discovery and image search, the lazy-loading images guide covers loading behavior, and the schema markup guide explains when an Article or Product image belongs in JSON-LD.
- 1Inventory images and separate missing alt attributes from intentionally empty alt values.
- 2Sample by template: hero, product gallery, article figure, logo link, icon button, and decorative media.
- 3Inspect the rendered DOM; CMS or JavaScript components may change the source value.
- 4Navigate with a screen reader or accessibility tree and confirm linked/icon images have useful names.
- 5Review image-search landing pages and high-value products manually for specificity and surrounding text.
- 6Fix the CMS component or content rule that produced the problem, then sample new and old records.
How DomainLens contributes
DomainLens identifies missing or suspicious image alternatives and exposes page-level image findings. Use that output to locate candidates, then make the human decision about purpose and context. The on-page SEO checklist places alt text beside surrounding copy, headings, and image performance.
- Does every image need descriptive alt text?
- No. Decorative images should normally use alt="" so assistive technology can ignore them.
- Is there an ideal alt-text length?
- There is no useful universal character target. Be concise enough for the task and move complex explanation into nearby content.
- Should alt text contain keywords?
- Only when the term naturally identifies the image. Keyword stuffing makes the alternative worse for users.