If your alt text doesn't provide a vision-impaired person with an experience equivalent to that of a sighted person, then it's not effective alt text.
It does not need headings and subheadings.
If your alt text doesn't provide a vision-impaired person with an experience equivalent to that of a sighted person, then it's not effective alt text.
It does not need headings and subheadings.
Your shared posts also need alt text. If you share a lot of things, but aren't adding alt text then you aren't actually accessible.
Your shared posts also need alt text. If you share a lot of things, but aren't adding alt text then you aren't actually accessible.