Don't explain things or give other information only in alt-text!

Generally, alt-text is only for a visual description of the image to which an alt-text belongs. Information not available in the post text and/or in the image itself must not go into alt-text.

This includes, but is not limited to:

• explanations
• author or creator credits
• license information

But why not?

That's because some people can't access alt-text. I'm being serious here.

Accessing alt-text requires a mouse (or something similar) or a touch screen or a screen reader. Sighted people don't have screen readers, so it's mouse (or similar) or touch screen for them.

But using a mouse (or similar) or a touch screen requires at least one working hand. And not everyone has working hands, just like not everyone can see properly. Those who don't have working hands can't read the explanations, the credits, the license information or anything else that isn't also available in the post text or the image. All this information is inaccessible and therefore lost to them.

Thus, such information must never go into the alt-text, always into the post text itself instead. Everyone who can access your post can access the post text. Nobody is excluded from the post text.

Even if you've only got 500 characters because you're on vanilla Mastodon, you must never use alt-text to write around your character limit. The article behind this link also tells you what to do instead if you need more than 500 characters.