useful list! I’ve got most of those bookmarked already, though it’s useful to see them all in other lists.
One thing that I did read somewhere (I think that it was a BBC report, but I can’t find it any more), is that for dyslexic users, having the alt text pop up over an image can be confusing, as it’s information they don’t need to read.
The article suggested that the best option is to use Title tags – for anything that you _really_ want to use as a tool tip (remembering that the ability to use Alt text as a tool tip was never intended) – so mostly the title tag would be empty. Then use the alt tag as intended.
The result is that for those who can see the images, where the alt text doesn’t add further information (which it shouldn’t anyway), they won’t get confused with the extra reading, but for those who can’t see the images, then they do get the additional information.