private void AddCropToElement(FrameworkElement element)
        {
            if (_frameworkElement != null)
            {
                RemoveCropFromCur();
            }

            Rect rect;
            if (_isRectSizeSet)
            {
                rect = new Rect(
                    _rectX,
                    _rectY,
                    _rectWidth,
                    _rectHeight);
            }
            else
            {
                rect = AutoFit(element);
            }

            var layer = AdornerLayer.GetAdornerLayer(element);
            _croppingAdorner = new CroppingAdorner(element, rect);
            _croppingAdorner.SlideWidth = this.GetCurrentPresentation().SlideWidth;
            _croppingAdorner.SlideHeight = this.GetCurrentPresentation().SlideHeight;
            _croppingAdorner.CropChanged += (sender, args) =>
            {
                var croppingRect = _croppingAdorner.ClippingRectangle;
                if (croppingRect.Width*croppingRect.Height < 1)
                {
                    SaveCropButton.IsEnabled = false;
                }
                else
                {
                    SaveCropButton.IsEnabled = true;
                }
            };
            Rect = rect;

            layer.Add(_croppingAdorner);
            _frameworkElement = element;
            SetClipColorGrey();
        }