Google's John Mueller said in the latest Search Off the Record podcast that you should leave decorative alt text on your images empty and blank. Oh, and John later said, the World Wide Web Consortium (W3C) also says you should do that.
At the 17: 13 mark in the podcast, John said "But once it gets into things like, "Oh, this is a concept," or like, "It's decorative," so it doesn't... There's some places that say, "Oh, you don't need to put alt text in a decorative image." Like if it's purely there just for aesthetics, then it's better to just leave the alt text empty."
Here is the embed:
As John pointed out on Twitter later the W3C also recommends this, as they wrote here:
Decorative images don’t add information to the content of a page. For example, the information provided by the image might already be given using adjacent text, or the image might be included to make the website more visually attractive.In these cases, a null (empty) alt text should be provided (alt="") so that they can be ignored by assistive technologies, such as screen readers. Text values for these types of images would add audible clutter to screen reader output or could distract users if the topic is different from that in adjacent text. Leaving out the alt attribute is also not an option because when it is not provided, some screen readers will announce the file name of the image instead.
Here is more of the context around this:
Wouldn't doing this leave you vulnerable to a website accessibility lawsuit? I know there was a firm taking some bloggers to court a few years back over this kind of thing.
— Josie (@P3bbelzz) October 12, 2022
https://t.co/QV2nERGXfb says similar things (whew): "Decorative images don’t add information to the content of a page. (...) In these cases, a null (empty) alt text should be provided (alt="") so that they can be ignored by assistive technologies, such as screen readers."
— ⛰ johnmu is not a cat ⛰ (@JohnMu) October 12, 2022
Forum discussion at Twitter.
Note: This was pre-written and scheduled to be posted today, I am currently offline for Simchat Torah.