Image preview for post when compiling from .Rmd with bookdown?

I realize the hugo side of this is covered in the documentation and my particular issue may be out of scope for this forum, since it deals with going from Rmarkdown to hugo, but here goes …

I’m compiling from .Rmd using the bookdown package in R, rather than simply building from .md. I understand that the preamble should include:


But the [header] part causes the .Rmd compile to fail and image: “path” alone seems to be ignored, as any random string can substitute without error message for the path of an actual image and in any case no preview appears.

So does any one on here have experience with this?