Wikimedia's image syntax should have separate fields for
the caption and for alternate text. Captions and
alternate text have opposite purposes: captions only make
sense if an image *is* visible, whereas alternate text is
intended for display only if the image is *not* visible. So
it doesn't make sense for them to use the same data.
The current effect, in screenreaders and in text-only
browsers, is two recitals of the same non-sequitur.