title: Using PIL to detect a scan of a blank page
body: <p>So I often run huge double-sided scan jobs on an unintelligent Canon multifunction, which leaves me with a huge folder of JPEGs. Am I insane to consider using PIL to analyze a folder of images to detect scans of blank pages and flag them for deletion?</p>
  
  <p>Leaving the folder-crawling and flagging parts out, I imagine this would look something like:</p>
  
  <ul>
  <li>Check if the image is greyscale, as this is presumed uncertain.</li>
  <li>If so, detect the dominant range of shades (background colour).</li>
  <li>If not, detect the dominant range of shades, restricting to light greys.</li>
  <li>Determine what percentage of the entire image is composed of said shades.</li>
  <li>Try to find a threshold that adequately detects pages with type or writing or imagery.</li>
  <li>Perhaps test fragments of the image at a time to increase accuracy of threshold.</li>
  </ul>
  
  <p>I know this is sort of an edge case, but can anyone with PIL experience lend some pointers?</p>