Sometimes deciding what the ALT text should be can lead to questions.
The 4Syllables decision tree found at: http://www.4syllables.com.au/2010/12/text-alternatives-decision-tree/ is summarized below. Reading that page as well is recommended.
Start with an image in the context of the webpage.
What does the image do or mean? Make decisions based on context and how the image functions on the webpage.
Is it purely decorative, like a line or banner? The ALT text should be closed quotes. Decision is ALT=””
Is it a sensory image like art or photography? The ALT text should describe the image and the image should be captioned. Decision is ALT=”description of the image”
Does the image present new information?
Is it a function or a link? The ALT text should explain what will happen for users who click on the image. Decision is ALT=”label for link”
Is the image simple to explain? Decision is ALT=”short explanation.” The explanation should be:
- accurate and equivalent,
- not redundant,
- and must not use the phrases “image of" or "graphic of” because the user and software can already identify it an image.
Is the image complex or wordy? A text explanation or description for the image can be provided on the same page as the image or the ALT text can lead users to a page which has only that description. Decision is ALT=”short explanation of the image plus a URL or location of the longer text description”
If the image has text in it, all text needs to be written out in the long description. The 4Syllables decision tree website explains the graphic tree in full directly below the image.