/// <summary>
        /// remove watermark from list
        /// </summary>
        /// <param name="selectedIndex"></param>
        /// <returns>
        /// Returns true if there is at least one watermark remaining; otherwise false.
        /// </returns>
        public bool RemoveWatermark(int selectedIndex)
        {
            if (this.watermarkCollection != null &&
                this.watermarkCollection.Count >= selectedIndex + 1)
            {
                WatermarkBase watermark = this.watermarkCollection[selectedIndex];
                watermark.PropertyChanged -= watermark_PropertyChanged;

                this.watermarkCollection.RemoveAt(selectedIndex);

                if (this.watermarkCollection.Count > 0)
                {
                    return(true);
                }
                else
                {
                    return(false);
                }
            }
            else
            {
                return(false);
            }
        }
 public void AddWatermark(WatermarkBase watermark)
 {
     watermark.PropertyChanged += new PropertyChangedEventHandler(watermark_PropertyChanged);
     this.watermarkCollection.Add(watermark);
 }