title: Inserting an image to ggplot2
body: <p>Is it possible to insert a raster image or a pdf image underneath a <code>geom_line()</code> on a <code>ggplot2</code> plot?</p>
  
  <p>I wanted to be quickly able to plot data over a previously calculated plot that takes a long time to generate as it uses a large amount of data.</p>
  
  <p>I read through this <a href="https://kohske.wordpress.com/2010/12/26/use-image-for-background-in-ggplot2/" rel="noreferrer">example</a>. However, as it is over one year old I thought there might be a different way of doing this now.</p>