Embedding graphics in a pdf()

I've had two reasons for wanting to embed graphics in R pdf output.

1. I am plotting something on top of a surface (It's actually a desk.) of
which I have a picture and would like to place a picture underneath.
2. I can produce all of my presentation slides in R without LaTeX but have a
few pictures that I need to include as slides. I would like to add images
inside the R script instead of manipulating them afterwards with Imagemagick
and pdftk.

Can these be done?

Tom