claude: Fix image alt text propagation to LaTeX for PDF accessibility

Preserve markdown image captions and fig-alt attributes as alt text
for \includegraphics[alt={...}] in LaTeX output. This enables PDF/UA
compliance by ensuring alt text is embedded in the PDF.

The fix preserves image captions as the alt attribute before clearing
them for figure handling. Also propagates fig-alt from FloatRefTarget
to Image elements for LaTeX output.

Closes #13248

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: gordonwoodhull

news/changelog-1.9.md

@@ -45,6 +45,7 @@ All changes included in 1.9:
 
 - ([#4426](https://github.com/quarto-dev/quarto-cli/issues/4426)): Add `pdf-standard` option for PDF/A, PDF/UA, and PDF version control. Supports standards like `a-2b`, `ua-1`, and versions `1.7`, `2.0`. Works with both LaTeX and Typst formats.
 - ([#10291](https://github.com/quarto-dev/quarto-cli/issues/10291)): Fix detection of babel hyphenation warnings with straight-quote format instead of backtick-quote format.
+- ([#13248](https://github.com/quarto-dev/quarto-cli/issues/13248)): Fix image alt text not being passed to LaTeX `\includegraphics[alt={...}]` for PDF accessibility. Markdown image captions and `fig-alt` attributes are now preserved for PDF/UA compliance.
 - ([#13661](https://github.com/quarto-dev/quarto-cli/issues/13661)): Fix LaTeX compilation errors when using `mermaid-format: svg` with PDF/LaTeX output. SVG diagrams are now written directly without HTML script tags. Note: `mermaid-format: png` is recommended for best compatibility. SVG format requires `rsvg-convert` (or Inkscape with `use-rsvg-convert: false`) in PATH for conversion to PDF, and may experience text clipping in diagrams with multi-line labels.
 - ([rstudio/tinytex-releases#49](https://github.com/rstudio/tinytex-releases/issues/49)): Fix detection of LuaTeX-ja missing file errors by matching both "File" and "file" in error messages.
 - ([#13667](https://github.com/quarto-dev/quarto-cli/issues/13667)): Fix LaTeX compilation error with Python error output containing caret characters.

src/resources/filters/layout/latex.lua

@@ -332,6 +332,10 @@ function latexCell(cell, vAlign, endOfRow, endOfTable)
     -- see if it's a captioned figure
     if image and #image.caption > 0 then
       caption = image.caption:clone()
+      -- preserve caption as alt attribute for PDF accessibility before clearing
+      if not image.attributes["alt"] then
+        image.attributes["alt"] = pandoc.utils.stringify(image.caption)
+      end
       tclear(image.caption)
     elseif tbl then
       caption = pandoc.utils.blocks_to_inlines(tbl.caption.long)
@@ -380,6 +384,10 @@ function latexCell(cell, vAlign, endOfRow, endOfTable)
     if image and #image.caption > 0 then
       local caption = image.caption:clone()
       markupLatexCaption(cell, caption)
+      -- preserve caption as alt attribute for PDF accessibility before clearing
+      if not image.attributes["alt"] then
+        image.attributes["alt"] = pandoc.utils.stringify(image.caption)
+      end
       tclear(image.caption)
       content:insert(pandoc.RawBlock("latex", "\\raisebox{-\\height}{"))
       content:insert(pandoc.Para(image))
@@ -658,9 +666,13 @@ end
 function latexImageFigure(image)
 
   return renderLatexFigure(image, function(figure)
-    
+
     -- make a copy of the caption and clear it
     local caption = image.caption:clone()
+    -- preserve caption as alt attribute for PDF accessibility before clearing
+    if #image.caption > 0 and not image.attributes["alt"] then
+      image.attributes["alt"] = pandoc.utils.stringify(image.caption)
+    end
     tclear(image.caption)
 
     -- get align

src/resources/filters/quarto-pre/figures.lua

@@ -38,6 +38,17 @@ end
           return float
         end
       elseif _quarto.format.isLatexOutput() then
+        -- propagate fig-alt to Image elements for LaTeX (enables \includegraphics[alt={...}])
+        local altText = attribute(float, kFigAlt, nil)
+        if altText ~= nil then
+          float.content = _quarto.ast.walk(float.content, {
+            Image = function(image)
+              image.attributes["alt"] = altText
+              return image
+            end
+          })
+          float.attributes[kFigAlt] = nil
+        end
         return forward_pos_and_env(float)
       end
     end,

tests/docs/smoke-all/pdf-standard/ua1-image-alt-text.qmd

@@ -0,0 +1,25 @@
+---
+title: "UA-1 image with alt text"
+lang: en
+pdf-standard: ua-1
+keep-tex: true
+_quarto:
+  tests:
+    pdf:
+      noErrors: default
+      ensureLatexFileRegexMatches:
+        # Alt text MUST be passed to \includegraphics[alt={...}] for PDF/UA
+        - ['\\DocumentMetadata\{', 'pdfstandard=\{ua-1\}', 'tagging=on', 'includegraphics\[.*alt=']
+        - []
+      printsMessage:
+        # Should NOT warn about missing alt text since we provided it
+        level: WARN
+        regex: "PDF accessibility:.*Missing alt text"
+        negate: true
+---
+
+# Test Document
+
+This image has alt text which should be passed through to LaTeX's `\includegraphics[alt={...}]` for PDF/UA compliance.
+
+![Test image description](test-image.png)