Sometimes standardization might have amusing consequences.

Some preliminary. Say the web author need to place an image for pure design purposes, it could be a background image for example, and of course the author doesn't want it to be visible for screen reader users. So the author can do:

This technique is well known and was standardized by Techniques for UAAG published at 2002:

In some authoring scenarios, empty content (e.g., alt="" in HTML) may make an appropriate text equivalent, such as when non-text content has no other function than pure decoration, or when an image is part of a "mosaic" of several images and does not make sense out of the mosaic.

Neither browser nor assistive technology is supposed to repair the text equivalent for empty alt image or in other words it should be no image from the user perspective. This technique was supported by Firefox and by number of screen readers over the years. On implementation level the trick is accessible name of the image element is an empty string what is interpreted by screen reader the image should be ignored.

Then after years as accessibility standardization process goes on we've got a quite good initiative which is HTML accessibility mapping. Among other things, it has HTML to ARIA mapping. This is nice but brings ARIA on the level of universal accessibility language while it barely fits all nuances of HTML markup. When it comes to HTML img alt="" case then the closest thing popping up in ARIA is role="presentation". Semantically it looks good, however it doesn't match the accessibility API mapping we used to have for years. The change can be made both on browser and screen reader sides but it doesn't have any practical benefit.

By the way the topic seems constantly bother accessibility minds through years. Not taking into account the fresh bug, we had same bug 4 years ago.