For each image conveying information that has a detailed description, is this description relevant?
A trend chart with a long description that just says 'Sales Evolution': this description exists on paper, but conveys nothing. Criterion 1.6 checked that a detailed description was in place. 1.7 goes further: is this description truly relevant?
A relevant description retranscribes the entirety of the visual information conveyed by the image. For a line graph: values, axes, legends, trends. For an infographic: each key data point in logical order. The criterion is simple to state. Difficult to succeed at in practice.
The audit method is straightforward: read the detailed description without looking at the image. If you lack data to understand the content, the description has failed. This criterion covers six types of elements: <img>, <input type="image">, <object>, <embed>, <svg> and <canvas>.
6 tests to assess the relevance of the detailed description
Relevance of detailed description <img>
- Identify all
<img>elements that have a detailed description (viaaria-describedby, an adjacent link, or linked visible content). - For each one, read the description without looking at the image.
- Verify that the description retranscribes all visual information conveyed by the image. No key data should be missing.
- If a description is incomplete, inaccurate, or merely repeats the
alt, the test fails.
Relevance of detailed description <input type="image">
- Identify all
<input type="image">elements that have a detailed description. - For each one, read the description without looking at the button image.
- Verify that the description faithfully retranscribes the visual information conveyed by the button image.
- If the description does not match what the image conveys, the test fails.
Relevance of detailed description <object>
- Identify all
<object type="image/…">elements that have a detailed description. - For each one, read the description without looking at the image.
- Verify that the description covers all visual information.
- An incomplete or inaccurate description fails the test.
Relevance of detailed description <embed>
- Identify all
<embed type="image/…">elements that have a detailed description. - For each one, read the description without looking at the image.
- Verify that the description faithfully retranscribes all visual information conveyed by the image.
- A vague or partial description fails the test.
Relevance of detailed description <svg>
- Identify all
<svg>elements that have a detailed description (via the child<desc>element,aria-describedby, or linked content). - For each one, read the description without looking at the SVG.
- Verify that the description retranscribes all visual information, including values and legends.
- If important visual data is missing from the description, the test fails.
Relevance of detailed description <canvas>
- Identify all
<canvas>elements that have a detailed description. - For each one, read the description without looking at the content rendered by the canvas.
- Verify that the description covers all visual information generated.
- A description that addresses only part of the content fails the test.
Examples
❌ Non-compliant : Chart with non-relevant description
<img
src="courbe-ventes-2025.png"
alt="Sales Curve 2025"
aria-describedby="desc-courbe">
<p id="desc-courbe">This chart illustrates company sales for the year 2025.</p>The description repeats word for word what the alt attribute already says. It provides no numerical values, no trends, no axis legends. A screen reader user knows a chart exists; they do not know its content. The description is present in technical terms, but non-relevant per criterion 1.7.
✅ Compliant : Chart with relevant detailed description
<img
src="courbe-ventes-2025.png"
alt="Sales Curve 2025"
aria-describedby="desc-courbe">
<p id="desc-courbe">Line chart, monthly sales from January to December 2025.
Horizontal axis: the 12 months of the year.
Vertical axis: revenue in thousands of euros, 0 to 500.
Overall upward trend. Notable values:
January 120k, March 180k (spring peak),
July 95k (summer trough), December 480k (year-end peak).</p>The description retranscribes axes, value ranges, overall trend, and key figures. A user who cannot see the chart obtains exactly the same information as one who views it. This is the relevance threshold targeted by the criterion.
Tips and pitfalls
⚠️ Repeating the alt in the detailed description
This is the most frequent error in audits of this criterion. The alt provides a short equivalent, a few words. The detailed description retranscribes all visual information. Writing 'Q3 2025 Sales Chart' in both fields is not a relevant description: it is repetition.
⚠️ Describing style rather than content
Writing 'Blue and orange chart with a legend in the bottom right' describes formatting, not information. The color of a bar has no value for a user who cannot see the image. Only data, trends, and meanings matter.
⚠️ SVG with <desc> element
For an <svg>, the child <desc> element can serve as a detailed description. Relevance is evaluated the same way: does <desc> retranscribe all visual content? A <desc> that says 'Pie chart' without citing the percentage of each slice is non-relevant, even if technically present.
💡 Structure the description like a data table
For complex charts, the most robust description reproduces the data in an adjacent HTML table linked via aria-describedby. This mechanism is both relevant, maintainable, and visible to all, not just screen reader users. Bonus: the table is also useful on mobile with slow connection, when the image does not load.
⚠️ Adjacent content serving as description
If a paragraph placed right after the image already describes its content in detail, it can serve as a detailed description. RGAA accepts this mechanism provided the link is established: via aria-describedby pointing to that paragraph, or a mention in the alt like 'see description below'. Relevance is evaluated identically.
Frequently asked questions
How do you assess the relevance of a detailed description per RGAA criterion 1.7?
Cover the image and read only the description. If you need to look at the image to complete your understanding, the description is insufficient. A relevant description renders the image unnecessary to obtain the information, not to see it.
What elements should appear in a detailed image description to satisfy RGAA?
All information-bearing details. A chart with 12 monthly values: each must appear. On the other hand, the color of bars should not be described if it is not semantic. The rule: describe everything whose absence would change content comprehension.
How do you visually hide a detailed description while respecting RGAA criterion 1.7?
A description hidden via display:none or visibility:hidden is not rendered by screen readers. To be accessible, it must be in the DOM and restitutable: either visible to all, or off-screen with the CSS clip technique, or accessible from an adjacent link or button. RGAA validates multiple mechanisms, provided the information is genuinely reachable.
How do you apply RGAA criterion 1.7 to <canvas> elements generated dynamically by JavaScript?
Yes. Regardless of whether the <canvas> is static or dynamically rendered, if the element conveys information, its detailed description must be relevant. For JavaScript-generated charts, the most robust solution is an adjacent HTML table updated at the same time as the canvas.
How do you efficiently audit RGAA criterion 1.7 on a site with many images?
First filter images that have a detailed description (presence of aria-describedby or an adjacent link). This is typically rare: most sites already fail criterion 1.6. On affected images, apply the coverage test: read the description alone and list missing information. A single absent data point is sufficient to fail the test.