showPsfrag is used to display (using ghostview) a postscript
  image that contained psfrag LaTeX strings, by building a small LaTeX
  script and running latex and dvips.
showPsfrag(filename)
name or character string or character vector specifying file prefix.
Frank Harrell
  Department of Biostatistics
  Vanderbilt University
  fh@fharrell.com
Grant MC, Carlisle (1998): The PSfrag System, Version 3.  Full
  documentation is obtained by searching www.ctan.org for pfgguide.ps.
postscript, par, ps.options,
  mgp.axis.labels, pdf,
  trellis.device, setTrellis