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WCAG: 1.1.1: Images must have alternate text
All images must have alternate text to convey their purpose and meaning to screen reader users.
Screen readers have no way of translating an image into words that gets read to the user, even if the image only consists of text. As a result, it's necessary for images to have short, descriptive
alttext so screen reader users clearly understand the image's contents and purpose.
If you can't see, all types of visual information, such as images, are completely useless unless a digital text alternative is provided so that screen readers can convert that text into either sound or braille. The same is true in varying degrees for people with low vision or color-blindness.
When you do not provide an acceptable alternative that works for their available sensory modalities, such as making an image accessible by providing a digital text description, screen readers cannot convert it into speech or braille to make it available by sound or touch.