alt is perfectly fine (and much better than a non-descriptive
alt), especially for (decorative) images that have no real meaning for the content:
If the image is not an active image [...] and if it doesn’t contain information [...] then it is a decorative image. Images that are only for decoration should not have any (descriptive) alt text, instead you should use the empty string as alt text.
If the alt attribute contains no text (
alt="") this tells screen readers to ignore the image. Screen reader users don't need to know about decorative images, it would just add to "audio clutter" on the page, so by assigning an empty alt text to an image the screen reader is told to ignore it.