In MediaWiki, alternative text is typically supplied through a combination of the thumbnail caption (not to be confused with the structured file captions) and the text supplied for the image alt parameter in the MediaWiki markup.

It is sometimes asked whether the alt could be defined centrally on the Wikimedia Commons file description page. There is currently no way to do that.

• phab:T21906 − “Allow default alternate text for images to be provided on the file description page”
• phab:T166094 − “Allow editors to provide default alt text on Wikimedia Commons file description pages”
• phab:T213585 − “Images (on articles, on file/category pages, and in the media viewer) should default to use their structured data alt text when available”
• d:Wikidata:Property proposal/alt tag – Stalled discussion about a dedicated alt attribute property.