alt Hacker NewsThe question to ask is, what a sighted person learns after looking at the image? The answer is the alt text. E.g if the image is a floppy, maybe you communicate that this is the save button. If it shows a cat sleeping on the windowsill, the alt text is yep: "my cat looking cute while sleeping on the windowsill".
I really like how you framed this as the takeaway or learning that needs to happen as what should be in the alt and not a recitation of the image. Where I've often had issues is more for things like business charts and illustrations and less cute cat photos.