title: When printing an image, what determines how large it will appear on a page?
body: <p>Using Python's Imaging Library I want to create a PNG file.<br>
  I would like it if when printing this image, without any scaling, it would always print at a known and consistent 'size' on the printed page.</p>
  
  <p>Is the resolution encoded in the image? </p>
  
  <p>If so, how do I specify it?</p>
  
  <p>And even if it is, does this have any relevance when it goes to the printer? </p>