AngularJS: Binding inside directives

I'm trying to acheive databinding to a value returned from a service inside a directive.

I have it working, but I'm jumping through hoops, and I suspect there's a better way.

For example:

<img my-avatar>

Which is a directive synonymous to:

<img src="{{user.avatarUrl}}" class="avatar">

Where user is:

$scope.user = CurrentUserService.getCurrentUser();

Here's the directive I'm using to get this to work:

.directive('myAvatar', function(CurrentUser) {
    return {
        link: function(scope, elm, attrs) {
            scope.user = CurrentUser.getCurrentUser();
// Use a function to watch if the username changes,
// since it appears that $scope.$watch('user.username') isn't working
            var watchUserName = function(scope) {
                return scope.user.username;
            };
            scope.$watch(watchUserName, function (newUserName,oldUserName, scope) {
                elm.attr('src',CurrentUser.getCurrentUser().avatarUrl); 
            }, true);
            elm.attr('class','avatar');

        }
    };

Is there a more succinct, 'angular' way to achieve the same outcome?

How about this ? plunker

The main idea of your directive is like

.directive('myAvatar', function (CurrentUserService) {
        "use strict";
        return {
            restrict: 'A',
            replace: true,
            template: '<img class="avatar" ng-src="{{url}}" alt="{{url}}" title="{{url}}"> ',
            controller: function ($scope, CurrentUserService) {
                $scope.url = CurrentUserService.getCurrentUser().avatarUrl;
            }
        };
    });