title: Show image with Express, instead of downloading it
body: <p>A <a href="https://github.com/stevage/tilelive_server" rel="nofollow">simple server</a> I'm working can serve images. When browsing to the image URL directly, Chrome offers to download the image, rather than just showing it in the browser. Why is that? Presumably it is something in the headers?</p>
  
  <p>The relevant code is this:</p>
  
  <pre><code>    tilestore.getTile(req.param("z"), req.param("x"), req.param("y"), function(err, tile) {
  
        if (!err) {
          res.send(tile);
        } else {
          res.send("Tile rendering error: " + err + "\n");
        }
  
      });
  </code></pre>
  
  <p>Do I need to add something to the headers? They are currently as follows:</p>
  
  <pre><code>HTTP/1.1 200 OK
  Server: nginx/1.4.6 (Ubuntu)
  Date: Mon, 01 Sep 2014 07:22:30 GMT
  Content-Type: application/octet-stream
  Content-Length: 37779
  Connection: keep-alive
  X-Powered-By: Express
  ETag: W/"9393-1937584155"
  </code></pre>