title: add local image file in R presentation
body: <p>I'm trying to include one imaging file (<code>.png</code>) using R markdown for R presentation.
  I followed the suggestion from: <a href="https://stackoverflow.com/questions/10517020/how-to-import-local-image-using-knitr-for-markdown">How to import local image using knitr for markdown</a>
  but by using <code>![title](my.png)</code>, I get this error:</p>
  
  <blockquote>
    <p>Error: unexpected '[' in "!["</p>
  </blockquote>
  
  <p>The <code>my.png</code> file is in current path. I also tried using absolute path but got the same error message.</p>
  
  <p>Putting above inside the r chuck failed too.</p>
  
  <p>I also tried </p>
  
  <pre><code>```{r,fig.width=350, fig.height=250,echo=FALSE}
  library(png)
  library(grid)
  appimg &lt;- readPNG('my.png')
  grid.raster(appimg)
  ```
  </code></pre>
  
  <p>but failed too!</p>
  
  <p>I am working on windows 7 R studio 0.98.1102 and R 3.2.1 .</p>