This demo uses HttpHandlerUrl property to specify a http handler to process the image.

Sample:

• Set HttpHandlerUrl property to "CustomBinaryImageHandler.ashx".
• The class CustomBinaryImageHandler inherits from C1BinaryImageHandler(class: C1.Web.Wijmo.Controls.C1BinaryImage.C1BinaryImageHandler)
  and overrides ProcessImageData method to customize the image:
  
  

  public class CustomBinaryImageHandler : C1BinaryImageHandler
  {
      public override C1BinaryImageData ProcessImageData(C1BinaryImageData imageData)
      {
          using (var outStream = new System.IO.MemoryStream())
          using (var inStream = new System.IO.MemoryStream(imageData.Data))
          using (var image = Bitmap.FromStream(inStream))
          {
              var newImage = AddWatermark(image);
              newImage.Save(outStream, ImageFormat.Png);
              imageData.Data = outStream.ToArray();
              imageData.MimeType = "image/png";
              imageData.ImageFileName += "_Watermark";
          }
  
          return base.ProcessImageData(imageData);
      }
  
      private Image AddWatermark(Image image)
      {
          var watermarkString = "ComponentOne";
          var font = new Font("Arial", 8F, FontStyle.Regular);
          var newImage = new Bitmap(image.Width, image.Height);
  
          using (var g = Graphics.FromImage(newImage))
          {
              g.DrawImage(image, new Point(0, 0));
              g.DrawString(watermarkString, font, new SolidBrush(Color.White), new PointF(2, newImage.Height - font.Height - 2));
          }
  
          return newImage;
      }
  }