When someone attaches a picture to their post, the SE system automatically attaches a tooltip Enter image description here, inviting the poster to give some alt-text for the image.
These tips are easy to overlook and the description is often not entered.
However, alt-text is used by browsers for the sight-impaired. The text is presented or spoken to the reader.
Several of our posts are being provided with alt-text, so thanks to those posters who are doing it, but there are a few without.
As I've said above, it is easy to overlook and no blame can be assigned.
Can I suggest we try to assist as many visitors to the site as possible by adding image descriptions. Just a word or two is all that is required.
Also, feel free to edit existing posts to add descriptions. I've done a couple but there are more to do.
Find them with search such as:
While we are a young site we can set an example to the rest of SE.
The issue is neither new nor unique to us - see for example ELU