How to Add Alternative Text to Images in a PDF
Standards this affects
- PDF/UA — ISO 14289-1, clause 7.3 (graphics)
- WCAG 2.1 — 1.1.1 Non-text Content (Level A)
- Section 508 — 502 / WCAG 2.0 AA by reference
What this means
Alternative text (alt text) is a short text description attached to an image so that screen readers can announce what the image shows. In a PDF, alt text lives on the figure tag in the structure tree.
Why it matters
A screen reader cannot interpret a picture — it can only read the alt text you provide. Without it, users who are blind or have low vision miss charts, logos, signatures, infographics, and any information carried by images. Missing alt text is one of the most common and most cited accessibility failures.
How the checker flags it
- The checker lists figures or images with no alternate text.
- Acrobat's accessibility check flags "Figures - Alternate text".
- A screen reader announces "image" or a filename instead of a description.
How to fix it
- 1
Decide if each image is meaningful or decorative
Meaningful images (charts, photos that convey information, logos with the company name) need alt text. Purely decorative images (borders, background textures) should instead be marked as artifacts so they are skipped.
- 2
Open the Set Alternate Text tool in Acrobat Pro
Go to All Tools → Prepare for accessibility → Set alternate text. Acrobat walks through each detected figure and gives you a box to type a description.
- 3
Write concise, informative descriptions
Describe the content and function, not the appearance. Keep it to a sentence or two. Don't start with "image of" — the screen reader already says it's a figure. For charts, summarize the takeaway (e.g. "Bar chart: revenue rose from $2M in 2023 to $5M in 2025").
- 4
Handle text inside images
If an image contains text (a scanned letter, an infographic), the alt text should include that text, or the content should be provided as real text elsewhere. Images of text fail WCAG 1.4.5.
- 5
Re-check and listen
Re-run the checker, then test with a screen reader (NVDA is free) to confirm each image announces sensibly in context.
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Frequently asked questions
- How long should PDF alt text be?
- Usually one or two sentences. Convey the meaning a sighted reader would get at a glance. For complex images like detailed charts, give a short alt text plus a longer description in the surrounding text or a data table.
- What about decorative images?
- Mark them as artifacts (in Acrobat: change the tag to an artifact, or use the Reading Order tool to set "Background"). Decorative images should not have alt text and should be skipped by assistive technology.