I've always meant to improve options for visually impaired users, and I'd love if this process could be simplified by Word Press.
One of these things is adding a longdesc attribute to images.
If you typed a description into an image you've just uploaded you could either tick a box or have a preference set in options to include the description as a long desc.
This could then create a page which would be linked to as part of the img element. I would have thought this might be reasonably easy to implement. I believe to be absolutely correctly implemented there should be a "d-link" as well, for older browser compatibility.
Additional information here: