Don't re-download images for each rendering format?

[KatherineCox]

How hard would it be to have the TOC-less render reuse the images from the bookdown render? Maybe checking if a file has been updated since this render action started?

If that's complicated, it's not a big deal, just a convenience. It would speed things up when I've got a lot of images.

Edit: I guess more generally, how hard would it be to reuse the output of R code? If there's slow code, it'd be nice if it didn't have to run twice. That's not something causing trouble for me personally yet, but I could see it being annoying for some books.