using System.Drawing.Drawing2D;
private void button3_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
  { this.button3.Cursor = Cursors.Hand;
         Bitmap bmpBob =(Bitmap)this.button3.Image;     
      GraphicsPath graphicsPath = CalculateControlGraphicsPath(bmpBob);
     this.button3.Region = new Region(graphicsPath); 
  }
  private static GraphicsPath CalculateControlGraphicsPath(Bitmap bitmap)
  {
  
   GraphicsPath graphicsPath = new GraphicsPath(); 
 
   Color colorTransparent = bitmap.GetPixel(0, 0);
 
   int colOpaquePixel = 0;
 
   for(int row = 0; row < bitmap.Height; row ++)
   {   
    colOpaquePixel = 0;
  
    for(int col = 0; col < bitmap.Width; col ++)
    {
   
     if(bitmap.GetPixel(col, row) != colorTransparent)
     {
     
      colOpaquePixel = col;
   
      int colNext = col;
   
      for(colNext=colOpaquePixel; colNext<bitmap.Width; colNext++)
       if(bitmap.GetPixel(colNext, row) == colorTransparent)
        break;
    
      graphicsPath.AddRectangle(new Rectangle(colOpaquePixel,
       row, colNext - colOpaquePixel, 1));
   
      col = colNext;
     }
    }
   } 
   return graphicsPath;
  }