Изображений - сколько угодно.
Спецификация:
https://html.spec.whatwg.org/multipage/grouping-co...
Пример из спецификации:
<figure>
<img src="castle1423.jpeg" title="Etching. Anonymous, ca. 1423."
alt="The castle has one tower, and a tall wall around it.">
<img src="castle1858.jpeg" title="Oil-based paint on canvas. Maria Towle, 1858."
alt="The castle now has two towers and two walls.">
<img src="castle1999.jpeg" title="Film photograph. Peter Jankle, 1999."
alt="The castle lies in ruins, the original tower all that remains in one piece.">
<figcaption>The castle through the ages: 1423, 1858, and 1999 respectively.</figcaption>
</figure>
Если группировать figure во вложенные figure, то и figcaption тоже может быть много(по одной на каждый figure).
Пример из спецификации:
<figure>
<figcaption>The castle through the ages: 1423, 1858, and 1999 respectively.</figcaption>
<figure>
<figcaption>Etching. Anonymous, ca. 1423.</figcaption>
<img src="castle1423.jpeg" alt="The castle has one tower, and a tall wall around it.">
</figure>
<figure>
<figcaption>Oil-based paint on canvas. Maria Towle, 1858.</figcaption>
<img src="castle1858.jpeg" alt="The castle now has two towers and two walls.">
</figure>
<figure>
<figcaption>Film photograph. Peter Jankle, 1999.</figcaption>
<img src="castle1999.jpeg" alt="The castle lies in ruins, the original tower all that remains in one piece.">
</figure>
</figure>