angular.module("fb_totem")
.controller('mycontroller', function($scope){
 $scope.loading=true;

 $scope.ImgLoaded=function(val){
    $scope.loading=false;
  }
})

<img image-on-load="ImgLoaded" ngf-humbnail="url_mobilePhoto"/>
 <button type="button" ng-click="cancel()" ng-disabled="loading"</button>

angular.module("fb_totem")
.directive('imageOnLoad', function() {
        return {
            restrict: 'A',
            link: function(scope, element, attrs) {
                element.bind('load', function() {
                    scope.$apply(attrs.imageOnLoad)(true);
                });
                element.bind('error', function(){
                  scope.$apply(attrs.imageOnLoad)(false);
                });
            }
        };
    })