<figure>
Content that can move without breaking the text around it.
The rule of thumb is in the name. If you can lift the block out of the flow and drop it into a sidenote, an appendix or another page without the neighbouring paragraph ceasing to make sense, it is a figure. It works for images, but also for code, tables, poems and diagrams.
<figcaption> is the caption, first or last child, and it becomes the accessible name of the whole figure. Without it, all that is left is the image's alt.
<figure>
<img src="/imagens/exsicata-042.jpg" alt="Leaf pressed on brown paper">
<figcaption>Sheet 042, collected in open country.</figcaption>
</figure>