how to make plot output to JPG or GIF

Hello,

How does one write PLOT() commands that make individual graphic files of
plots that are currently generated to the graphics output window of a
session?

Currently, I have a chron-job that generates a new data input files once
every hour. My goal is to then automatically run my "source.r" file with
the plot commands which then automatically generates a web-ready graphic
file in a folder for my server.

thanks!
-revansx