This post is a page bundle. The bigimg entry forest.jpg is resolved as a page resource, so the image can live in the same directory as index.md.
Images in a bundle are also processed by Hugo. The thumbnail above is cropped to a square for the post list, the header image is capped at bigimgWidth, and the figure and gallery below get resized variants with a srcset:
Plain Markdown images get the same treatment. This one is a page resource, so it has a srcset:
A width attribute on the next line sets the display size and caps the generated variants:
This one is under static/, so it is served unchanged:
