Function rather than image description, charts, photos with captions, logos and decoration: how to find the right alt text for every image in a PDF – and why AI suggestions always need a review by someone who knows the subject.
Alt text (alternative text) replaces an image for people who cannot see it. It says what the image conveys in its context – not what it looks like. The guiding question is: what would be missing if the image were not there? This is required by WCAG 1.1.1 (Non-text Content); in a PDF, the alt text is stored in the Alt entry of the Figure tag (WCAG technique PDF1). PDF/UA-1 requires it for every image tagged as a figure. Images without informational content are instead marked as artefacts (PDF4).
What kind of image is it?
The W3C’s images tutorial distinguishes a few cases that also help with PDFs:
- Informative images: photos, illustrations, icons that communicate something. Short alt text stating the message.
- Decorative images: ornamental borders, backgrounds, mood images without a message. Artefact, no alt text.
- Functional images: linked logos or icons. The alt text names the destination or the function, not the appearance.
- Text in images: the alt text contains the text – in full if it matters for the content.
- Complex images: charts, maps, organisation charts. A short key message plus a detailed description in the document.
Function before description – examples
- Photo of a ground-breaking ceremony. Weak: ‘Photo of several people with spades.’ Better: ‘The mayor and representatives of the developer at the ground-breaking ceremony for the day-care centre on Lindenweg.’
- Telephone icon in front of a telephone number. If ‘Telephone: …’ is written next to it, the icon is decorative and becomes an artefact. Alt text reading ‘telephone receiver’ would merely duplicate it.
- Logo of a funding programme. The name of the programme or organisation – nothing more. The colours of the logo do not matter.
- Poster as an image. The alt text gives the event, date and venue, i.e. the text of the poster.
Length and style
- Short: usually one sentence, rarely more than two.
- No ‘image of’ or ‘graphic shows’ – the screen reader already announces that a graphic follows.
- Do not repeat anything that is written in the text right next to it.
- End with a full stop; this creates an audible pause.
- Write in the language of the document, without file names such as ‘IMG_2034.jpg’.
Photos with captions
If a photo has a caption, the caption often already carries the message. The alt text then does not need to reinvent it. If software adopts the caption as alt text – DokAudit does this for photos with captions – that is a safe starting point: the message is correct, and no image remains silent. If the photo shows more than the caption says, add exactly that part to the alt text.
Charts and complex graphics
- Short alt text: type of chart and key message, for example ‘Bar chart: the number of day-care places has risen every year since 2022; the figures are in Table 3.’
- Detailed description: the data also belongs in the document as a table or text – right next to the chart or in the appendix, with a cross-reference.
- Maps and plans: describe what matters for the purpose – location, boundaries, routes – and not every street.
- Organisation charts: reproduce them as a nested list in the text; the alt text refers to it.
Decorative images, logos and coats of arms
In a PDF, a decorative image is not given empty alt text but is taken out of the structure as an artefact. This also applies to the logo or coat of arms that recurs in the running header on every page – running headers and footers are artefacts anyway. If, on the other hand, the logo appears once on the title page and identifies the publisher, it is informative and gets the name of the organisation as its alt text. Incidentally, logos are exempt from the contrast requirements (WCAG 1.4.3); their colours do not have to be adjusted.
Alt text with AI
AI image descriptions are good at recognising what can be seen in an image. But they do not know why it is in the document: what point a chart is meant to support, who the people are, whether an image is merely decoration. They can misread figures in charts and tend to speculate about the age, feelings or origin of the people shown. AI suggestions are therefore a draft, not a finished solution. Before approval, someone who knows the content checks:
- Is the statement correct – especially figures, names and places?
- Does it fit the purpose of the image in the document?
- Does it contain speculation about people that does not belong there?
- Does it duplicate the caption or the text next to it?
- Would the image be better off as an artefact?
Common mistakes
- Alt text such as ‘image’, ‘graphic’ or a file name.
- The caption is repeated word for word as a second description, with no added value.
- Decorative elements get alt text (‘blue wave’) instead of being artefacts.
- A chart is simply called ‘chart’ – the message is missing.
- Text in an image is not reproduced.
- AI suggestions are adopted without review.
How DokAudit helps
DokAudit marks decorative elements as artefacts, adopts the caption as alt text for photos with captions and suggests alt text for the remaining figures using AI. These suggestions are explicitly intended for review: the test report shows which images have alt text and where a review by the responsible department is needed. No machine can judge whether a text is accurate in substance – that remains with the department. How to check and improve alt text is part of the introduction in our training courses.
Sources:
As of: 09/2026. This article gives a general overview and is not legal advice. The legal and standards texts in force are authoritative; in individual cases, the law of the German states (Länder) may differ.