In my opinion, too many questions and too many answers rely on images and videos. To be accessible to the visually impaired, authors who use images in their questions and answers should write something along the lines of

Rant over.
alt text
is for cases when the image cannot be shown - text browser, file not available, iirc for the screen readers for the visually impaired - and should say what the image represents;title text
(which I supposecaption
translates to) is for when you hover over the image and it shows "additional" text which you will see together with the image. But browsers make it a bit hard because for historical reasons some may show one in place of the other when only one of them is defined. $\endgroup$