ALT Text: CLICK THE IMAGE. There’s text beneath it. (In my case, LOTS of text.) CLICK THE TEXT- the entire text appears. That’s how this works.

To POST ALT Text - upload your image, then CLICK it - a space appears and you type your text there. Simple. Set it up as a default in your Settings, that way you never have to think about it: settings > accessibility > require alt-text for images.