public async Task IdentifyCelebrityAsync()
        {
            try
            {
                if (this.ImageUrl != null)
                {
                    this.AnalysisResult = await VisionServiceHelper.AnalyzeImageAsync(this.ImageUrl);
                }
                else if (this.GetImageStreamCallback != null)
                {
                    this.AnalysisResult = await VisionServiceHelper.AnalyzeImageAsync(this.GetImageStreamCallback, new VisualFeature[] { VisualFeature.Categories }, new string[] { "Celebrities" });
                }
            }
            catch (Exception e)
            {
                ErrorTrackingHelper.TrackException(e, "Vision API AnalyzeImageAsync error");

                this.AnalysisResult = new Microsoft.ProjectOxford.Vision.Contract.AnalysisResult();

                if (this.ShowDialogOnFaceApiErrors)
                {
                    await ErrorTrackingHelper.GenericApiCallExceptionHandler(e, "Vision API failed.");
                }
            }
        }
        public async Task AnalyzeImageAsync(bool detectCelebrities = false, IEnumerable <VisualFeature> visualFeatures = null)
        {
            try
            {
                if (visualFeatures == null)
                {
                    visualFeatures = DefaultVisualFeatures;
                }

                if (this.ImageUrl != null)
                {
                    this.AnalysisResult = await VisionServiceHelper.AnalyzeImageAsync(
                        this.ImageUrl,
                        visualFeatures,
                        detectCelebrities?new string[] { "Celebrities" } : null);
                }
                else if (this.GetImageStreamCallback != null)
                {
                    this.AnalysisResult = await VisionServiceHelper.AnalyzeImageAsync(
                        this.GetImageStreamCallback,
                        visualFeatures,
                        detectCelebrities?new string[] { "Celebrities" } : null);
                }
            }
            catch (Exception e)
            {
                this.AnalysisResult = new Microsoft.ProjectOxford.Vision.Contract.AnalysisResult();

                if (this.ShowDialogOnFaceApiErrors)
                {
                    await ErrorTrackingHelper.GenericApiCallExceptionHandler(e, "Vision API failed.");
                }
            }
            finally
            {
                this.ComputerVisionAnalysisCompleted?.Invoke(this, EventArgs.Empty);
            }
        }