This translation has not been editorially reviewed yet. The German version is authoritative. Deutsche Fassung →
Image alt text from an SEO perspective: what it does and doesn't do
Alt text is the most important signal for what an image shows — for screen readers and for image search alike. The check verifies its presence; whether the text captures the image's content is decided by a human.
- From an SEO perspective, alt text is the only reliable text source for an image. Anyone who leaves it out gives up image search as an access path.
- The temptation to stack search terms in there is old, and it does double harm: search engines recognise it, and a screen reader reads the list out loud. What's spam to one is noise to the other.
- The accessibility-law part of the same topic is on the alt-text article — that covers empty alt text for decorative images, and why an automated test can't judge quality.
FAQ
Does the file name help in addition?
A descriptive file name does no harm and can act as a weak signal. It doesn't replace alt text, though — a screen reader only reads it aloud if nothing else is there, and usually unintelligibly at that.
How many search terms belong in alt text?
None. Describe what's visible. If the right term shows up naturally while doing that, good; forcing it in isn't.