title: Ng-src doesn't update in AngularJS view
body: <p>I'm using the following code in my Angular app to display an image:</p>
  
  <pre><code>&lt;img ng-src="{{planet.image_url}}" class="planet-img"/&gt;
  </code></pre>
  
  <p>And I'm using <code>$watch</code> to change the <code>image_url</code> attribute when other events happen. For example: </p>
  
  <pre><code>$scope.$watch('planet', function(planet){
    if (planet.name == 'pluto') {
       planet.image_url = 'images/pluto.png';
    }
  });
  </code></pre>
  
  <p>Using console logs, I see that the model attributes are changing just like I want them to, but these changes are not reflected in the DOM. Why isn't ng-src updating automatically as the model changes? I'm new to Angular, so maybe this is a concept I haven't yet grasped. Any help will be greatly appreciated.</p>