this.KeyPreview = true;

this.MouseWheel += new MouseEventHandler(Form1_MouseWheel);

void Form1_MouseWheel(object sender, MouseEventArgs e)
        {
   if (e.Delta > 0)
            {
                ShowPrevPicture();
            }
   else
            {
                ShowNextPicture();
            }
        }

protected override bool ProcessDialogKey(Keys keyData)
        {
   switch (keyData)
            {
       case Keys.Left:
       case Keys.Up:
                    ShowPrevPicture();
           return true;
       case Keys.Right:
       case Keys.Down:
       case Keys.Enter:
                    ShowNextPicture();
           return true;
       case Keys.Delete:
                    DeleteCurrentPicutreFromHardDisk();
           return true;
       case Keys.Subtract:
                    DownImageLevel(PictureList.ElementAt(curIndex));
                    DeleteCurrentPicutureFromShowList();
           return true;
       case Keys.Add:
       case Keys.Insert:
                    UpImageLevel(PictureList.ElementAt(curIndex));
                    DeleteCurrentPicutureFromShowList();
           return true;
            }
   return false;
        }