What alt text is, and who relies on it
Alt text is a short written description attached to an image in the page’s code. Most people never see it. A screen reader reads it aloud to someone who is blind or has low vision. It also appears when an image fails to load, and search engines and AI tools use it to understand what a picture shows.
Providing it is the very first rule in WCAG, success criterion 1.1.1, at Level A, the most basic level. Every Canadian accessibility standard that points to WCAG includes it. My WCAG basics guide explains how those levels work.
Say what the picture is for
The best test I know is this: if you had to replace the image with one sentence, what would that sentence say? That is your alt text. Some examples:
- Not helpful: “IMG_4032.jpg”, “image” or “photo”. They tell the listener nothing.
- Not helpful: “best plumber Duncan BC plumbing Cowichan Valley”. Stuffing keywords into alt text makes the page worse for people and does not fool Google.
- Helpful: “Owner fitting a new water heater in a customer’s basement.”
- Pictures of words, such as a sale banner, need alt text that includes the words themselves.
- A logo or image that is a link should describe where it goes, such as “Home” or your business name.
- A chart needs its main point in the alt text, with the full figures in the text nearby.
Keep it short, usually a sentence or less. There is no need to start with “image of”, because a screen reader already announces that it is an image.
When the right alt text is nothing
Some images are just decoration: a background pattern, a divider line, a stock photo that adds mood but no information. These should have an empty alt attribute, written alt="". That tells the screen reader to skip the image altogether.
Empty is not the same as missing. If the alt attribute is left out entirely, many screen readers fall back to reading the file name, which is how a listener ends up hearing “DSC underscore 0 0 4 1 dot jpeg”. And if an image already has a caption that says the same thing, the alt text does not need to repeat it.
Checking your own site
WordPress and most website builders have an “Alternative Text” field for each image in the media library. Start with your homepage and your most-visited pages. WebAIM’s free WAVE tool will flag every image that is missing alt text.
Many tools now write alt text automatically using AI. Treat that as a first draft. AI can describe what is in a photo, but it does not know why you put it there. The same goes for overlay plugins that promise to fix accessibility for you, which I explain in why accessibility overlays don’t work. A person who knows the page should always have the last word.