How to write good alt text for images
Blind or visually impaired people cannot see images on your site or in your document. Therefore, it is important that you provide images with alternative text. But how do you write such text? Find out here.
Alternative text or alt text gives meaning to visual content for people who cannot see it. In such text, you provide a brief description of what is to be seen. Screen readers read that text aloud so that people with visual impairments can understand the information. In short, it is an important way to make your content accessible. Not surprisingly, it is success criterion 1.1.1 of the WCAG.
When is an alt text necessary?
Alternate text is not always necessary. You don't need to use a text alternative if an image is meant to be decorative only. Such as a mood photo that shows something different than what the content is about. This includes CAPTCHA images, icons and spacers. Unsure if an image needs alt text? Then use the alt decision tree by W3C.
What does an alt text need to meet?
Concise and clear
First, alt text for informative images should be concise, but as long as necessary. Otherwise, users will be overwhelmed with information. You don't have to put “image of” or “picture of.” in it. A screen reader will already indicate that it is an image.
For functional images such as a printer icon, the alternative text should clearly state what the function is. Again, keep it concise, but understandable.
Are you dealing with complex images with a lot of information, such as graphs and diagrams? Then the text alternative may be longer. Moreover, it is better to describe such images in the body of the text. You can refer to this description in the alt text.
The essence supplemented with relevant details
A text alternative should contain the essence of the image. Consider what the image adds to the context. Then look for details that convey the message. Incorporate those into the alt text if it adds something.
Be careful not to include a value judgment in your text alt, for example, that a painting is beautiful or ugly. After all, that is an opinion and not a factual description of the image.
Alt text is often used, or rather misused, to include keywords. Keep in mind that the alt text is intended for users with disabilities. So use keywords in the alt text only if it actually fits the image.
Tips for good alternative text
In summary, here are the main points to watch out for when writing alternative text:
- Use alt text if the image contains and adds information to the body of the text;
- Keep the alt text concise but also as long as necessary;
- State the function of functional images such as buttons;
- Describe graphics or complex images in the main text;
- Incorporate keywords in the alt text only if appropriate to the image.
