title: Google App Engine (Python) Image Object Error
body: <p>I've extensively searched for an answer to this, and havent come up with anything close. I'm using google app engine to create a form that accepts 2 image files. Then i'd like to take them, get the difference between them, and save that to a blob that i will display beside the two uploaded images. </p>
  
  <p>I'm getting this error "img2 = abs(img1 - img2) TypeError: unsupported operand type(s) for -: 'Image' and 'Image'" in this chunk of code: </p>
  
  <pre><code>img1 = images.Image(blob_key=blob_info.key())
  blob_reader = blobstore.BlobReader(blob_info2.key())
  img2 = images.Image(blob_key=blob_info2.key())
  img3 = abs(img1 - img2)
  </code></pre>
  
  <p>Any help would be appreciated. I tried using the ImageChops difference but it says  so i just took the line from that function and put it directly in my code (being this line: abs(img1 - img2))</p>