<picture>
Several image sources; the browser picks one.
<picture> draws nothing: it is a wrapper of <source> elements that must end in an <img>. The browser walks the list, stops at the first source it accepts and hands the result to the img, which remains responsible for the alt and the layout.
It is for swapping the crop of a photo on a phone or offering AVIF with a JPEG fallback. If the only difference is file size, srcset and sizes on the <img> itself will do.
<picture>
<source media="(min-width: 60rem)" srcset="/imagens/exsicata-larga.avif" type="image/avif">
<source srcset="/imagens/exsicata.avif" type="image/avif">
<img src="/imagens/exsicata.jpg" alt="Sheet 042 on brown paper">
</picture>