Alternative Content
Alternative content is an equivalent that replaces non-textual content to make it perceivable by everyone. The alt attribute on an image is its most well-known form, but the concept also covers captions, text transcriptions, and audio descriptions. WCAG makes it their very first principle.
When discussing accessibility, "alternative content" is often reduced to the alt attribute of an image. The concept is much broader: every non-textual content on your page — image, video, audio, complex graphic — must have an equivalent perceivable by those who cannot access the original.
#Far Beyond Image alt
The WCAG divides alternative content requirements into two guidelines:
- Guideline 1.1: text alternative for all non-textual content. This is the
altof images, but also the accessible name of an icon button or CAPTCHA. - Guideline 1.2: alternatives for time-based media. Nine criteria cover captions, transcriptions, and audio descriptions.
In practice:
| Content | Expected Alternative |
|---|---|
| Informative image | Alternative text (alt) |
| Video with audio | Synchronized captions |
| Video without audio | Transcription or audio description |
| Audio only (podcast) | Text transcription |
| Complex graphic | Long description (aria-describedby or dedicated link) |
<!-- Captions on a video -->
<video controls>
<source src="demo.mp4" type="video/mp4">
<track kind="captions" src="demo-en.vtt" srclang="en" label="English">
</video>What many ignore: at WCAG Level A, criterion 1.2.3 offers a choice between audio description and full descriptive transcription. If producing an audio description seems too costly, a transcription that also describes visual elements fulfills the requirement.
#The Mistake: Stopping at alt
The majority of RGAA audits report issues on theme 1 (Images). Theme 4 (Multimedia) is often overlooked. A site can have flawless alt attributes and zero captions on its videos.
Automatic captions are not enough either. The W3C recommends human review: proper names, technical vocabulary, and passages in foreign languages are regularly mistranscribed.
Another pitfall: confusing captions with transcription. Captions help deaf people while watching video. Transcription allows deafblind people to access content via a braille display, and search engines to index it. Two distinct needs.
#In Summary
Alternative content is not limited to image alt attributes. Each media on your page requires its own alternative: text for images, captions for videos, transcription for audio. The RGAA dedicates two entire themes to it, and WCAG makes it their very first principle: content must be perceivable.