[R] Add png image outside plot borders

[Amelia McNamara]

I am trying to add a copyright disclaimer outside the plot borders of
some images I have created. I can use mtext() to add the written
portion, but I would like to have the Creative Commons license image
(http://en.wikipedia.org/wiki/File:Cc.logo.circle.svg) before the
text. I've found that I can plot a .png image inside the plot
boundaries using rasterImage() but I can't figure out how to do it
outside the boundaries.

Any help would be great. If you know unicode or Adobe Symbol encoding
for the CC logo, that might work too.

~Amelia McNamara
Statistics PhD student, UCLA