Accessibility

How to Write Meaningful Alt Text for Educational Publishing (STEM & Charts)

April 12, 2026·7 min read

Alternative text (alt text) is a fundamental pillar of digital accessibility. According to WCAG Success Criterion 1.1.1 (Non-text Content), all meaningful images must include a text equivalent for users relying on screen readers.

For a lifestyle blog, writing alt text is simple: "A golden retriever catching a frisbee." But for educational publishers, academic presses, and STEM (Science, Technology, Engineering, and Mathematics) content, writing meaningful alt text for complex diagrams, flowcharts, and graphs is a massive challenge.

Here are the best practices for writing alt text for complex publisher content.

1. Differentiate Between Decorative and Meaningful Images

The first rule of alt text is knowing when not to write it.

If an image is purely decorative (e.g., a swirl design marking a chapter break, or a stock photo that adds no educational context), it should be marked as decorative so assistive technologies ignore it.

In EPUB/HTML: `alt=""` or `role="presentation"`

In PDF: Tagged as an `Artifact`

2. The Formula for Complex Graphics

For complex graphics like charts or diagrams, standard alt text is often insufficient. A good practice is to provide a brief high-level summary in the `alt` attribute, and then link to a longer description (using `aria-describedby` or an extended description link).

The approach:

**Identify the image type:** "Bar chart..."

**State the main takeaway:** "...showing a 40% increase in revenue..."

**Provide the data (in the extended description):** "...with the Y-axis representing millions of dollars and the X-axis representing fiscal quarters..."

### Example: A Line Graph of Global Temperatures

Bad Alt Text: "Line graph showing temperature."

Good Alt Text: "Line graph titled 'Global Temperature Anomalies 1880-2020', showing a sharp upward trend starting around 1980." (Followed by a data table in the main text).

3. Handling Math and Scientific Equations

Images should never be used to display mathematical formulas. Screen readers cannot interpret an image of an equation.

Instead, STEM publishers must use MathML (Mathematical Markup Language). MathML allows assistive technologies to read equations logically—for instance, announcing "fraction with numerator a plus b, and denominator c."

If, for legacy reasons, an equation must be an image, the alt text must dictate the equation exactly as it should be spoken mathematically.

4. Flowcharts and Organizational Diagrams

Flowcharts inherently rely on visual structure (arrows and boxes) to convey meaning. To make them accessible:

Summarize the start and end points in the alt text.

Convert the structural flow into nested bullet points or an ordered list within an extended description.

5. Don't Rely Exclusively on AI

While AI models can do a decent job describing general photography, they frequently hallucinate or misinterpret specific data points in custom STEM charts and complex diagrams. Relying entirely on automated alt text generation for textbook publishing is a fast track to failing accessibility compliance. Human review by subject matter experts remains critical.

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If your editorial team is overwhelmed by the sheer volume of images requiring alt text remediation, schedule a free consultation with Holograph Press Works today. Let’s make your content accessible, compliant, and ready for the future.

Holograph Press Works remediates EPUB and PDF files to WCAG 2.2 AA and EPUB Accessibility 1.1 standards using our HoloRemedi platform. Every project includes official Ace and PAC3 PDF compliance reports. [Request a consultation →](/contact-us)