title: convert background image to grayscale - on the fly
body: <p>I can't seem to find exactly what I am looking for, so maybe one of you can help me. </p>
  
  <p>I'm trying to convert a background image of a div from color to grayscale. Uploading a version of it is not an option as this would be millions of photos a day, and storage capacity could be huge.</p>
  
  <p>These images are stored on Facebook in color, and I would like to grab them and change them to grayscale and display them, or perhaps overlay the entire container in grayscale or something like that. </p>
  
  <p>Any ideas/solutions?</p>
  
  <p>This can be done using HTML5 canvas.</p>