‘Alt text‘ for images is definitely worth including as often as we can, not only to help certain website visitors, but to improve SEO too. As we might expect, Google want us to use it as it’s meant to be used, describing the image and not trying to ‘game the system’ in any way. This is likely to be a sensible strategy.
It’s recommended that we don’t just describe the image, but also include why it’s there. So while ‘alt text’ saying ‘A picture of a blue widget’ might be adequate, it’s better to think about the context. Why is there an image of a blue widget on the page? What would you have to add to the text if there was no image there? If it’s a product page, better ‘alt text’ might be something like: ‘a blue widget, the fastest model in the broad range from BWCo, showing its full extension’.