title: Blur part of an Image and blend it with the Background
body: <p>I need to blur faces to protect the privacy of people in street view images like Google does in Google Street View. The blur should not make the image aesthetically unpleasant. I read in the paper titled <strong>Large-scale Privacy Protection in Google Street View</strong> by Google (<a href="http://static.googleusercontent.com/media/research.google.com/en//archive/papers/cbprivacy_iccv09.pdf" rel="nofollow">link</a>) that Google does the following to blur the detected faces.</p>
  
  <blockquote>
    <p>We chose to apply a combination of noise and aggressive Gaussian blur that we alpha-blend smoothly with the background starting at the edge of the box.  </p>
  </blockquote>
  
  <p>Can someone explain how to perform this task? I understand Gaussian Blur, but how to blend it with the background?  </p>
  
  <p><em>Code will be helpful but not required</em>  </p>
  
  <p>My question is not <em>how to blur a part of image</em>?, it is <em>how to blend the blurred portion with the background so that blur is not unpleasant</em>? Please refer to the quote I provided from the paper.  </p>
  
  <p>I have large images and a lot of them. An iterative process as in the possible duplicate will be time consuming. </p>
  
  <p><strong>EDIT</strong> </p>
  
  <p>If someone ever wants to do something like this, I wrote a Python implementation. It isn't exactly what I was asking for but it does the job.<br>
  Link: <a href="https://github.com/abdulfatir/pyBlur" rel="nofollow">pyBlur</a></p>