@TAV @futurebird if it's someone else's image or a screenshot then I think just descriptive.
If it's your own image I think you can add your own flavour to the alt text. You know what you were trying to say with the image, the things that are important in it so add all of that.
I don't have visual impairment, but in am neuro diverse and I'll often read the alt text to see what I should be getting from a picture.