Sobre el uso correcto de figure y figcaption
En How do you figure? se explica el uso correcto de las etiquetas figure y figcaption:
A figcaption is not a substitute for alt textY el artículo realiza un análisis del soporte de estas dos etiquetas por parte de varios lectores de pantalla.
Regarding images used within figures, one of the biggest misunderstandings of using a figcaption is that it’s used in place of image alternative text. Such a practice is outlined in HTML 5.2 as being a last ditch effort to convey meaningful information, but only when images are published without an author being able to provide appropriate alt text.
From the guidance of HTML 5.2:
Such cases are to be kept to an absolute minimum. If there is even the slightest possibility of the author having the ability to provide real alternative text, then it would not be acceptable to omit the alt attribute.
A figcaption is meant to provide a caption or summary to a figure, relating it back to the document the figure is contained within, or conveying additional information that may not be directly apparent from reviewing the figure itself.
If an image is given an empty alt, then the figcaption is in effect describing nothing. And that doesn’t make much sense, does it?