When it is used
Put a token in the src of an <img> and nanoesis infers an image field. At publish it processes the original into responsive sizes and formats and wraps it in a <picture> for you.
It is inferred from the tag, so you do not opt in. Add an alt token in the same tag for accessible alt text.
Example
A token in an img src becomes an image picker:
<img src="{hero}" alt="{caption}">In the editor
In the editor this is an image picker: upload or choose an image, with a preview.
You never think about sizes or formats; nanoesis generates the responsive variants when the site is published.