Figure has bbox

Figure has bbox is a check in recent versions of PAC, the free PDF Accessibility Checker. It fails when a Figure tag (the structure tag for an image, chart or diagram) doesn't record where its image sits on the page. That position is called a bounding box, or BBox: four numbers giving the left, bottom, right and top edges of the figure in PDF page units.

What this means

A Figure tag carries more than alt text, the description a screen reader reads in place of the image. The PDF specification (ISO 32000) defines BBox as a layout attribute for figures, formulas, forms and tables, and it expects one on a figure that sits entirely on one page. PAC checks for it on figures and reports this error when it's missing. People often search for the message together with the words "PDF/UA figure". PDF/UA is the ISO standard for accessible PDFs that PAC tests against.

Most tools write the box automatically when they create a figure. It tends to go missing when:

• a tag was changed to Figure by hand, for example by retyping a P tag in the Tags panel;
• an empty Figure tag was created first and the image dragged into it;
• the PDF came from a tool, or an older version of a tool, that doesn't write layout attributes.

Why it matters

Reflow (rewrapping text to fit a narrow screen or a large font) and tools that convert a PDF to other formats use the bounding box to find a figure and resize it. Without it, an image can be skipped or shown in the wrong place. Includoc maps this to WCAG 2.1 success criterion 1.4.10 Reflow for that reason. The people most affected are those who use reflow or magnification, often people with low vision. The bounding box also matters for compliance: a single missing box keeps a file from a clean PAC report.

How to fix it in Acrobat Pro and re-check in PAC

Acrobat doesn't show a figure's bounding box as a simple field, so the practical fix is to re-create the tag.

Fix it in the source file

Fixing the source is better when the document will be updated again:

• Word: Microsoft's Word PDF accessibility documentation (opens another website) says recent builds of Word include bounding box information in Figure tags. Older builds don't, which is a common reason figures exported from Word fail this check. Update Word, then export again with Document structure tags for accessibility turned on.
• Other tools: export a test page with one image and open it in PAC. If the figure passes, fix future versions in the source and export again rather than patching the PDF.
• Any app: give images their alt text in the source, so the exported Figure tag has both its description and its position.

Fix it automatically with Includoc

Includoc adds a bounding box to every figure automatically, using the area where its image is drawn on the page. This part needs no review.

What you still confirm is the alt text. A correct bounding box doesn't make a figure accessible on its own, so every figure's description goes to the review screen for you to approve or edit.

Standards

This is a PDF specification and PAC requirement rather than a WCAG success criterion in its own right. We map it to WCAG 2.1 1.4.10 Reflow because reflow is where a missing box causes trouble.

Related errors

• Figure tag: everything a correct Figure tag needs under PDF/UA.
• Figures alternate text – Failed: Acrobat's check for figures with no description.

To see how this check fits the wider standard, read PDF/UA explained, or check a PDF free to find figures without a bounding box.