Which WCAG Principle a Missing Alt Attribute Actually Breaks
A product photo on an e-commerce listing page ships with no alt
attribute at all. A sighted shopper glances at the photo and moves on in
under a second; a screen-reader user reaches the same image and hears
nothing describing what it shows.
Which WCAG POUR principle does this specific failure violate?
The correct answer is "Perceivable."
Perceivable means information must be presentable to users regardless of
which sense they rely on — an image's visual content needs an alt
description so a blind user can perceive it too, exactly what SC 1.1.1
(Non-text Content) requires. Without it, the information exists but is
imperceptible to that user, which is the defining Perceivable failure.
Operable is about controlling the interface, not perceiving content, so it doesn't apply — nothing about interacting with the image is broken. Understandable covers clarity of already-perceived information, but the image was never perceived at all here. Robust is about consistent interpretation across assistive technologies, a different failure than content being missing outright.
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