AngularJS directive attribute not rendering value when observed

I'm having trouble retrieving the value of an attribute passed in to a directive. My understanding of how directives work probably has something to do with this but it's my assumption that this is a scope related issue.

If you check the code below you'll see the attribute is being used as such:

display="contest.StyleBgImageMedia.filename" 

This value of contest.StyleBgImageMedia.filename is a string and I've verified it exists by consoling it our from the controller. The problem is that when trying to access it within the directives link function I can't retrieve the value but only the attribute name.

This directive is used in the view like such:

<uploader class="pull-left" action="builder/uploadMediaFile" display="contest.StyleBgImageMedia.filename" data-file="style_bg_image_media_id"></uploader>

The full directive has been posted below. You'll see that I'm using $observe to render the value of the display attribute but this isn't working.

app.directive('uploader', function($rootScope) {
    return {
        restrict: 'E',
        scope: {
            action: '@',
            display: '@display'
        },
        link: function(scope, elem, attrs) {
            elem.find('.fake-uploader').click(function() {
                elem.find('input[type="file"]').click();
            });

            scope.progress = 0;

            attrs.$observe('display', function(value) {
                if (value) {
                    scope.avatar = value;
                }
            });

            scope.sendFile = function(el) {
                var $form = jQuery(el).parents('form');
                if (jQuery(el).val() === '') {
                    return false;
                }

                $form.attr('action', scope.action);
                scope.$apply(function() {
                    scope.progress = 0;
                });

                $form.ajaxSubmit({
                    type: 'POST',
                    uploadProgress: function(event, position, total, percentComplete) {
                        scope.$apply(function() {
                            scope.progress = percentComplete;
                        });
                    },
                    error: function(event, statusText, responseText, form) {
                        $form.removeAttr('action');
                    },
                    success: function(responseText, statusText, xhr, form) {
                        var ar = jQuery(el).val().split('\\'),
                            filename =  ar[ar.length-1];

                        $form.removeAttr('action');
                        scope.$apply(function() {
                            scope.avatar = filename;
                        });

                        var response = jQuery.parseJSON(responseText);
                        $rootScope.$broadcast('file-uploaded', {
                            'model': attrs.file,
                            'file': response.message
                        });
                    }
                });

            };
        },
        replace: false,
        templateUrl: 'builder/views/partials/upload.php'
    };
});