Add image captions and "alt" texts to all images #9
Description
We should consider the following improvements over the original HTML:
- Whereever appropriate, we should add _image captions_ to images which didn't have them in the original HTML.
- We should add _"alt" texts_ to ALL images (which become visible when mouse-hoovering above them). If we can't think of anything better, we should use the image's file name (as appearing in the companion code block as output file name) as "alt" text.