Alt-text for images is not embedded in PDF output for accessibility

[sbwiecko]

I have:

• searched the issue tracker for similar issues
• installed the latest version of Quarto CLI
• formatted my issue following the Bug Reports guide

Bug description

Hello Quarto Team,

I've encountered an issue where alternative text (alt-text) for images is not being included in the final PDF output. This makes the resulting documents inaccessible to users who rely on screen readers.

The problem occurs for both figures generated from code chunks (e.g., Python) and for images included directly with Markdown syntax. I have confirmed that the alt-text is correctly rendered when exporting to HTML and EPUB formats, so the issue appears to be specific to the PDF rendering pipeline.

I have searched the existing issues on the repository and found several that deal with alt-text problems, but they seem to primarily focus on the DOCX format, for example:

• fig-alt removed by Quarto at least for docx (works with Pandoc) #5514

Minimal reproducible example

---
title: "Accessibility Test"
format:
  pdf:
    papersize: a4
---

This is a test to see if PDF tagging works.

```{python}
#| label: fig-testplot
#| fig-cap: "A simple test plot."
#| fig-alt: "This is the alternative text for the simple test plot that a screen reader should find."

import matplotlib.pyplot as plt

plt.plot([0, 1, 2], [2, 1, 3])
plt.title("Test Plot")
plt.show()
```

![A test image with alt-text](https://upload.wikimedia.org/wikipedia/commons/d/dd/Gray_book.png){fig-alt="A figure alt-text example."}

Actual behavior

The images in the generated PDF have no associated alternative text. The accessibility checker in Adobe Acrobat reports that the PDF file isn't tagged

Screenshot of the PDF accessibility check showing "PDF balisé (tagged PDF in English): Non (No)"

Expected behavior

The PDF's accessibility tree should contain tags for both images, and these tags should include the alt-text specified in the .qmd file. A screen reader should announce the alt-text when it encounters the images.

Your environment

• VSCode v1.103.1
• Windows 11 (25H2)
• One MiKTeX Utility 1.11 (MiKTeX 25.4)

Quarto check output

Quarto 1.7.33
[>] Checking environment information...
      Quarto cache location: C:\Users\Sébastien\AppData\Local\quarto
[>] Checking versions of quarto binary dependencies...
      Pandoc version 3.6.3: OK
      Dart Sass version 1.85.1: OK
      Deno version 1.46.3: OK
      Typst version 0.13.0: OK
[>] Checking versions of quarto dependencies......OK
[>] Checking Quarto installation......OK
      Version: 1.7.33
      Path: C:\Program Files\Quarto\bin
      CodePage: 65001

[>] Checking tools....................OK
      TinyTeX: (not installed)
      Chromium: (not installed)

[>] Checking LaTeX....................OK
      Tex:  (not detected)

[>] Checking Chrome Headless....................OK
      Using: Chrome found on system
      Path: C:\Program Files\Google\Chrome\Application\chrome.exe
      Source: Windows Registry

[>] Checking basic markdown render....OK

[>] Checking Python 3 installation....OK
      Version: 3.12.10
      Path: C:/Users/Sébastien/Documents/.env/Scripts/python.exe
      Jupyter: 5.7.2
      Kernels: python3, ir, ir4.4, julia-1.7

[>] Checking Jupyter engine render....OK

[>] Checking R installation...........OK
      Version: 4.5.1
      Path: C:/PROGRA~1/R/R-45~1.1
      LibPaths:
        - C:/Program Files/R/R-4.5.1/library
      knitr: 1.50
      rmarkdown: 2.29

[>] Checking Knitr engine render......OK

Thank you for your work on Quarto and for looking into this important accessibility feature.

[mcanouil]

That's actually a Pandoc issue:

• Accessibility mode for LaTeX jgm/pandoc#5409

And it is being track in a more general issue on Quarto side:

• Support PDF/A-compliant output using pdfx package #4426

[sbwiecko]

The other thing that may be relevant to this issue is that the intermediate TEX file generated by Quarto makes no mention of alt text anywhere, we don't see it in \includegraphics for example.

[mcanouil]

That's the issue from Pandoc.
Pandoc's default writer do not write those or any other accessible features for PDFs.

The Word issue you mentioned is different because Pandoc is writing the alt-text but Quarto's figure processing removes it.

[sbwiecko]

Thank you @mcanouil for the explanation and confirmation that I wasn't doing anything wrong. Can I close the issue then?

[mcanouil]

Let's keep it open and let maintainers decide if they want to keep only the general issue or also a more specific one to ensure it is handled at some point.

[cscheid]

We were going to make this fix for 1.8, but we need a Pandoc update to 3.7.0.2, and it seems that Pandoc changed the Markdown reader sufficiently much that we're now unfortunately blocked.

[cscheid]

#13249 is the Pandoc update PR.