I feel like screen-reader-capable text should always have two options, since so many things in life benefit from a detail option: “give me the tl;dr” with an option for “more” if I want it.

I know it’s hard enough to get consistent support for "alt" at all but an "alt-long" might be nice too so you can say things like alt="Picture of ocean landscape" alt-long="An evening shot of a beach in the Maldives, with a full moon, no clouds and still water.".