The alt description for photos is important, too. I didn’t realize this until recently, but one of the reasons that this is important is for ADA compliance. If you want your website to be ADA compliant, which you should because it’s a law now.
There’s a whole thing online about how you can get up to speed.
Having an alt description is important for visually impaired bled people. For example, if there’s somebody that is blind and they hover over a photo, their speech software will read the alt description. It’s important that this explains what the photo is of. Then Google in turn uses that as part of their SEO.
I would imagine that it also indexes Google images and things?
It does, yes. It’s a big player in helping Google index images.