This does not change size of the image in pixels, nor does it affect
appearance – it is lossless compression. This requires GraphicsMagick
(recommended) or ImageMagick to be installed.
Usage
resize(filename, geometry)
Arguments
filename
Name of image to resize.
geometry
Scaling specification. Can be a percent, as in "50%",
or pixel dimensions like "120x120", "120x", or "x120".
Any valid ImageMagick geometry specifation can be used.
Examples
if (interactive()) {
# Can be chained with webshot() or appshot()
webshot("http://www.google.com/", "google-small-1.png") %>%
resize("75%")
# Generate image that is 400 pixels wide
webshot("http://www.google.com/", "google-small-2.png") %>%
resize("400x")
}
providing 
.