Thank you, @AmauryH, but yes, I need a solution that applies anywhere in the post/page.
My parents are 73 and 75 years old, and are non-technical. They will want to drop images into their posts, and because of their cameras etc the images they take are large ~8MB+.
They will not cope with Markdown image actions, and I cannot rely on them to do any processing of the images before uploading.
So I would like to keep it stupidly simple (KISS) for them.
I would like a default settling - like the config quality setting - which sets a maximum image width size when drag & dropping it from their admin.
It is not perfect (an automatic srcset solution would be best), but at least this will stop their pages being a massive - ~40MB+ assuming they do their usual 5 or so images per “dairy” post.
types:
defaults:
type: file
thumb: media/thumb.png
mime: application/octet-stream
image:
filters:
default:
- [resize, 1000] <-- *this is what I added to set widths*
- enableProgressive <--*this was already there*